Chapter III: Part II: 1, The os occipitale (1, dorsal; 2, two lateral; 3, ventral (2)

The proximal end of the metatarsus is ossified from one center of ossification forming an epiphysis which caps the ends of the three original metatarsal bones that coalesce, first with one another, then with the epiphysis, thus forming a single compound bone. Above and just to the inside of the metatarsus there may occur a small bone which is imbedded in ligaments and articulates with the inner proximal surface of the metatarsus. This has been called by Gadow a _sesamoid bone_.

The shaft shows _tendonal grooves_ which are best marked on the posterior surface. The shaft is rounded at the sides and flattened on the anterior and posterior surfaces. At the juncture of the middle and inferior thirds of the metatarsus there is a conical process turned slightly backward, which serves as a base for the _spur_. The spur is a horny structure.

At the distal extremity occurs the threefold trochlear arrangement mentioned above, which incloses the fossa intercondyloidea. The inner trochlea is the broadest, and the outer the narrowest. The inner trochlea articulates with the proximal end of the second, the middle with the third, and the outer with the fourth toe.

=The Phalanges.= _Location._—Most domestic fowls are provided with four digits, or toes; the Houdan and Dorking are provided with five. In fowls with four toes the three principal toes, the second, the third, and the fourth, are directed forward, and the first, or hallux, is directed backward.

_Description._—The last phalanx of each toe, called the ungual phalanx, is slightly curved downward, is pointed anteriorly, like the claw of the cat or dog, and is covered with a horny sheath. The articular ends of the joints of the phalanges are enlarged. The base of the basal phalanx has two enlargements, the superior-inferior tubercles, or tuberculum superius et inferius, between which is located the fossa articularis transversa. Laterally the head has two condyles, condyli laterales, which are divided by the sulcus longitudinalis. The bodies of the phalanges vary in form; they are superiorly rounded, but inferiorly rounded, flat, or even somewhat concave. The distal extremity has an articular trochlea.

The _first toe_, or digit, called the _great toe_, or _hallux_, is composed of three phalanges, or segments. The first segment, or basal phalanx is considered a rudimentary metacarpal bone; it is attached by a fibrous cartilaginous tissue to the inner posterior surface of the inferior extremity of the metacarpal bone just below the spur.

The _second toe_, likewise composed of three phalanges, is directed forward. It articulates with the inner trochlea located on the inferior metacarpal bone.

The _third toe_, made up of four phalanges, is the middle of the three forward toes. It articulates with the middle trochlea of the inferior extremity of the metacarpal bone.

The _fourth toe_, is composed of five phalanges; it is, however, of approximately the same length as the third, the segments being shorter. The fourth or outer toe articulates with the outer trochlea of the distal extremity of the metacarpal bone.

ARTHROLOGY

=Kinds of Joints.=—Joints may be movable, immovable, or mixed. In _movable_, or _true joints_ the articular surface of each bone is covered by cartilage. The bones are held together by ligaments, the capsular one often surrounding the joint and enclosing the synovial membrane. In some joints there is a pad of fibrous cartilage interposed between the two articular cartilages. Such a pad, called a _meniscus_, adds to the elasticity and the free movement of the joint. Movable joints form the most numerous class; they are for the most part found in the limbs.

In an _immovable joint_ there is only a thin layer of fibrous or cartilaginous material interposed between the bones. The fibrous layer of the periosteum of both bones unite to cover the connecting material and becomes attached to the same, thus serving as a ligament. If the connecting material is fibrous, the joint is called a _suture_; if cartilaginous, a _synchondrosis_. These joints are found in the skull and in the pelvis.

The term _mixed_ is used with reference, not to the motion in joints, but to their structure, which partakes of the nature of both the movable and immovable. The bones are firmly joined by a strong interposed pad of fibrous cartilage to which also is adherent the ligaments of the joint. There are no capsular ligaments; the cartilaginous pad or disc is softer toward its center, where occasionally there may be one, or even two, narrow cavities. Authorities differ as to whether such cavities are lined by synovial membrane or not. Since there are really no frictional surfaces in such a joint, motion depends upon the flexibility of the disc. The joints between the vertebral centra afford the best illustration of the mixed class.

=Movement of Joints.=—The movements admissible in joints may be divided into four kinds: gliding, angular movement, circumduction, and rotation. These movements are often, however, more or less combined in the various joints. It is seldom that there occurs only one kind of motion in any particular joint.

_Gliding movement_ is the most simple kind of motion that can take place in a joint, one surface gliding or moving over another without any angular or rotary movement.

_Angular movement_ occurs only between the long bones. By it the angle between the two bones is increased or diminished. It may take place in four directions: forward and backward, consisting of flexion and extension; or inward and outward from the medial line of the body, consisting of adduction and abduction. Abduction of a limb is movement away from the medial line of the body. Adduction of a limb is movement toward the medial line of the body.

_Circumduction_ is that limited degree of motion which takes place between the head of a bone and its articular cavity, whilst the extremity and sides of the limb are made to circumscribe a conical space, the base of which corresponds with the inferior extremity of the limb, the apex with the articular cavity; this kind of motion is best seen in the shoulder- and hip-joint.

_Rotation_ is the movement of a bone upon an axis, which is the axis of the pivot on which the bone turns, as in the articulation between the atlas and axis, when the odontoid process serves as a pivot around which the atlas turns; or else is the axis of a pivotlike process which turns within a ring, as in the rotation of the radius upon the humerus.

_Pronation_ is a form of rotation in which the inferior extremity of the radius passes before the ulna, and thus causes the hand to execute a kind of rotation from without inward.

_Supination_ is a form of rotation in which the movement of the forearm and hand are carried outward so that the anterior surface of the latter becomes superior.

=The Ligamentous Structure.=—Ligaments are dense, fibrous, connecting structures. They are made up principally of white fibrous tissue and exist in all true joints.

There are four kinds of ligaments associated with true joints:

The first kind, the _capsular ligament_ which encloses all true joints, is thin and consists of interlaced fibers attached to the bone at the edges of the articular cartilages. It either partly or wholly surrounds the joint, enclosing and protecting a synovial apparatus, which, by secreting a liquid resembling serum, lubricates the joint to prevent friction.

The second kind, the binding or _lateral ligaments_, consist of flattened or rounded cords or bands of fibrous tissue. Such a ligament extends from one bone to the other, and firmly attached to their roughened surfaces, holds the bones in place and at the same time allows the required amount of motion.

The third kind, located between the joints, is called _interosseous ligament_.

The fourth kind, called the _annular ligament_ binds down and protects the tendons.

=Ligaments of the Ear[2].=—The concha of the ear is provided with a superior and an inferior ligament.

Footnote 2:

The classification of Gadow is used.

=Ligaments of the Jaw.=—The articulations of the lower jaw are complex. The freely movable articulation is between the inferior maxilla and the quadrate. Less freely movable articulations are formed by the quadrate with the temporal, the zygomatic and the pterygoid. A lateral ligament of the jaw, the _articulo-jugale_ extends from the posterior border of the inner wing of the os articulare of the inferior maxilla (Fig. 8, No. 10, and Fig. 19, No. 15) to the outer border of the os quadrato jugulare.

A _lateral temporo-maxillary ligament_ extends from the outer surface of the temporal bone to the outer border of the os articulare of the inferior maxilla (Fig. 8, No. 11, and Fig. 19, No. 14).

=Ligaments of the Vertebræ.=—In each space between the bodies of the vertebræ there is a _meniscus intervertebralis_. This meniscus is analogous to the annulus fibrosus of mammals (Gadow), which, is possibly formed as a protrusion of the anterior surface of the vertebral body. The meniscus or disc may develop into a ring-shaped structure, the true meniscus, or it may develop to different degrees as an extension of the vertebral body surface, and become, as in the dorsal and lumbar regions, fused with the vertebral segments, in which case it is called the annulus fibrosus.

The vertebral disc which is connected with the atlas and which is fused with that bone, represents the first meniscus, which is called the _ligamentum transversum atlantis_. This, as well as other ligaments of the spinal column, may become ossified.

The ligament which is located between those vertebral bodies which face each other and is inside the joint cavity, is called the _ligamentum suspensorium corporum vertebralium_. It passes through the central opening of the meniscus and lies exactly in the long axis of the body of the vertebra.

The first ligament of the neck is the _ligamentum suspensorium dentis epistrophei_. The _ligamentum capsulare atlantico-occipitale_ and the _ligamentum capsulare atlantico-epistrophicum odontoideum_ are two parts of the joint capsule of the vertebral body. Other ligaments of this part are the _membranæ obturatoriæ intervertebrales posteriores_, which are located between the semicircular rims of the neck vertebræ.

The _ligamentum transversum atlantis_ surrounds the occipital condyle.

The _ligamentum nuchæ_ is a thin, membranous, ribbon-like structure which lies between the muscles of the right and those of the left side of the middle, and the lower part on the posterior of the neck, and ends in attachments to the superior spines of the cervical vertebræ.

The _ligamentum elasticum interspinale profundum_ and the _ligamentum elasticum interspinale superficiale_ and the three last named are the ligaments which keep the neck of the fowl in the s-shape, without the action of the muscles.

The _ligamentum capsulare obliquum_ connects the facets of the oblique processes.

=Ligaments of the Ribs.=—The thick inferior end of the sternal portion of the true rib has two small articular heads, which articulate with two depressions in the articular surface of the sternum. This articulation is held firm by a _capsular ligament_.

The upper end of the sternal rib forms an almost perfect right angle with the inferior end of the dorsal rib with which it is connected by a joint provided with a synovial apparatus and a capsular ligament. This arrangement allows free movement outward and inward and is the main joint in respiration.

The upper end of the dorsal portion of the rib articulates with the dorsal vertebra. The joint formed by the articular head with the body of the vertebra is provided with a capsular ligament. The tubercle of the rib articulates with the facet on the transverse process of the dorsal vertebra, and is provided with a transverse ligament, called the _ligamentum transversum externum_. It is also provided with a capsular ligament.

The _ligamentum triangulare_ connects each processus uncinatus with the succeeding rib. This ligament is in the form of a membranous sheet, or aponeurosis.

=Ligaments of the Sternum= (Fig. 13).—The external and the internal notches of the sternum are bridged over with a thin membrane which gives an extensive surface for muscular attachments. The sternal muscles overlie this portion.

FIG. 13.—Muscles of the fore extremity. Inside view. 1, Lateral
external process of sternum. 2, Lateral internal process of same. 3,
Ligament of the external notch. 4, Ligament of the internal notch.
5, Pectoralis major. 5_a_, Its fan-shaped expansion at
shoulder-joint laid back. 6, Pectoralis tertius. 7, The coracoid. 8,
Biceps. 8_a_, Its long head. 8_b_, Its short head. 9, Pectoralis
secundus. 10, Rectus abdominis. 11, Teres et infraspinatus. 12,
Deltoid. 13, Capsular ligament. 14, Teres minor. 15,
Coraco-brachialis. 16, Serratus magnus anticus. 17, Extensor
metacarpi radialis longior. 18, Pronator brevis. 19, Flexor carpi
ulnaris. 20, Flexor carpi ulnaris brevior. 21, Flexor digitorum
profundus. 22, Extensor indicis longus. 23, Extensor ossis metacarpi
pollicis. 24, Humerus. 25, Shoulder. 26, Elbow. 27, Carpus. 28,
Section through vertebra. 29, Keel of sternum. 28_a_, Flexor brevis
pollicis. 29_a_, Extensor proprius pollicis. 30, Flexor minimi
digiti brevis. 31, Interosseous palmaris. 32, Interosseous palmaris.
]

The sternum is connected by a fibrous mass with the inferior portion of the clavicle, or hypocledium (Fig. 57), the _claviculosternal ligament_.

The inferior narrow elongated end of the coracoid forms with the sternum a true articulation, which is provided with a capsular ligament, the _ligamentum capsulare_. Capsular ligaments occur at the articulations between the sternum and ribs.

=Ligaments of the Shoulder-joint= (Fig. 13).—The shoulder-joint is made up of the scapula, the humerus, and the coracoid. The ends of these three bones form the _foramen triosseum_ (Fig. 15, No. _A_, 7) through which passes the tendon of the elevator muscle of the wing.

The furcula, independent of the shoulder-joint or girdle, is attached to the supero-internal part of the proximal end of the coracoid by fibrous connective tissue; it is also connected to the other bones of the shoulder-joint by the _ligamentum coraco-furculare_ and the _ligamentum furculo-scapulare_.

The _ligamentum coraco-scapulare_ extends from the tuberosity of the furcula to the coracoid and to the processus furcularis of the scapula.

The _ligamentum coracoido-scapulare externum_ extends between the external tuberosity of the coracoid, the tuberosity of the scapula, and the humerus.

The _ligamentum coracoideo-scapulare inferius_ extends from the coracoid to the inner tubercle of the scapula.

Another long, broad ligament belongs to the episternal apparatus.

The shoulder-joint is provided with a wide, loose, _capsular ligament_ (Fig. 13, No. 13). Attached to the humerus are four other ligaments, of which three pass from the anterior end of the coracoid and the fourth from the scapula. The latter are as follows: first, the _supero-anterior ligamentum humero-coracoideum_, which extends from the small tubercle of the humerus to the coracoid bone; second, the _antero-inferior ligamentum humero-coracoideum_, which extends from the humerus to the coracoid; third, the _ligamentum coraco-humerale_, which extends from the coracoid to the large tubercle of the humerus; fourth, the _ligamentum humero-scapulare_ which extends between the processus humeralis of the scapula and the head of the humerus.

=Ligaments of the Elbow-joint= (Fig. 14).—The elbow-joint is made up of the ulna, radius and the humerus. The ligaments of the elbow-joint are as follows: the _ligamentum capsulare cubiti_, or capsular ligament, which extends from the processus cubitalis of the humerus to the processus olecranalis coracoideus of the ulna and to the tuberositas radii of the radius (Fig. 15, No 5).

The _ligamentum laterale cubiti externum_ connects the outer humeral distal extremity with the head of the radius (Fig. 15, No. 2).

The _ligamentum laterale cubiti internum_ lies between the inner distal extremity of the humerus and the tuberculum internum of the ulna (Fig. 14, No. 9).

The _ligamentum annulare radii_ originates on the olecranon, surrounds the head of the radius, and is attached to the tuberculum internum of the ulna (Fig. 15, No. 3).

The _ligamentum cubiti teres_ extends from the head of the radius to the upper end of the ulna (Fig. 15, No. 4).

FIG. 14.—Muscles and ligaments of the arm and forearm of a hen.

_A._ External view. 1, Expansor secundarium. 2, Tensor patagii longus.
3, Tensor patagii brevis. 5, Brachialis anticus. 6, Pronator longus.
7, Supinator brevis. 8, Extensor indicis brevis. 10,
Scapulo-humeralis.

_B._ Internal view. 9, Ligamentum laterale cubiti internum.
]

The _ligamentum transversum_ spreads out between the head of the ulna and the radius, thus uniting the two bones, and limiting supination (Fig. 15, No. 1).

=Ligaments of the Carpal Joint.=—The carpal joint is made up of the ulna, radius, the two carpal bones and the metacarpus.

There are two strong _ligamenta obliqua carpi ulnaris_ which extend from the processus styloideus of the ulna to the tuberculum posterius carpi ulnaris of the os carpi ulnaris.

The _ligamentum posticum ulnare carpi ulnaris_ extends from the processus styloideus of the ulna to the os carpi ulnaris.

FIG. 15.—Ligaments of the arm and forearm of a hen.

_A._ The scapulo-coraco-humeral articulation. 1, Proximal end of the
humerus. 2, Articular head of humerus. 3, The coracoid. 4, Proximal
end of the clavicle. 5, Tendon of pectoralis tertius. 6, Tendon of
pectoralis secundus. 7, Opening or foramen triossium through which
the tendon of the elevator of the wing passes. (Pectoralis
secundus.) 8, Broken end of scapula.

_B._ 1, Ligamentum transversum. 2, Ligamentum laterale cubiti
externum. 3, Ligamentum annulare radii. 4, Ligamentum cubiti teres.
5, A portion of the ligamentum capsulare cubiti. 6, Distal extremity
of humerus. 7, Ulna. 8, Radius.

_C._ Muscles of the outside surface of the arm. 1, Tensor patagii
longus. 2, Extensor digitorum communis. 3, Tensor patagii brevis. 4,
Anconeus. 5, Flexor carpi ulnaris. 6, Biceps. 7, Triceps. 8.
Deltoid. 9, Brachialis anticus. 10, Flexor metacarpi radialis. 11,
Extensor ossis metacarpi pollicis. 12, Extensor metacarpi radialis
longior. 13, Extensor indicis longus.
]

The _ligamentum ulnare carpi radialis_ is a short ribbon-like ligament which passes over the above-mentioned ligaments and is attached to the inner surface of the os carpus radialis.

The _ligamentum ulnare carpi radialis internum_ is a strong ligament which originates on the inner part of the elbow. It extends to the upper rim of the base of the main digit.

The _ligamentum radiale carpi radialis externum_ originates on the outside of the head of the middle digit and inserts to the superior tuberculum carpi radialis of the radius.

The _ligamentum carpi radialis internum_, a short ligament, extends from the inside of the head of the main digit to the inner rim of the carpi radialis.

The _ligamentum carpi interosseum_ is located between the carpal bones.

The _ligamentum ulnare metacarpi internum_ is spread out between the processus styloideus of the ulna and the tuberositas muscularis on the upper side of the middle finger base at a point where the second and the third metacarpi separate.

The _ligamentum ulnare metacarpi externum_ extends from the tubercle of the distal extremity of the ulna, on the dorsal side, to the tubercle on the base of the metacarpus.

_Ligamentum radiale metacarpi_ extends from the head of the inner digit to a point near the tuberculum muscularis of the radius.

The _ligamentum transversum ossis carpi radialis et metacarpi_ is located between the inferior tuberculum ossis carpi radialis and the first metacarpal bone.

There is another ligament between the tuberculum superiorus carpi radialis and the first metacarpal bone.

The _ligamentum ossis carpi radialis internum et metacarpi_ extends from the inner surface of the carpus radialis to the tuberositas muscularis of the radius.

The _ligamentum ossis carpi ulnaris externum et metacarpi_ extends from the ulnar carpal bone to the tuberculum of the metacarpal bone.

The _ligamentum ossis carpi ulnaris internum et metacarpi_ extends from the processus uncinatus of the ulnar carpal bone to the tuberositas muscularis of the metacarpal bone.

=Ligaments of the Finger.=—The _ligamentum pollicare_ connects the thumb with the first metacarpal bone.

The _ligamentum anterius ossis metacarpi et primæ phalangis digiti secundi_ extends from the tuberculum articulare metacarpi, of the proximal end of the metacarpus, to the tuberculum articulare of the first phalanx of the second or large finger. Similarly attached, are also an internal and a posterior ligament, or _ligamentum internum_ and _ligamentum posterius_.

The three phalanges are all provided with capsular ligaments, or ligamenta capsularia, which bind together the several phalanges.

The small or third finger is connected to the metacarpus by a capsular ligament, the _ligamentum capsulare_, and by an interosseous ligament, or _ligamentum interosseum digitorum_, to the first phalanx of the second finger.

=Ligaments of the Pelvis.=—The obturator foramen, formed by the ilium and the ischium, is covered by a broad membranous ligament (Fig. 4, No. 29).

The oblong foramen, or foramen oblongum, and the foramen ischiadicum, formed by the ischium and the pubis are covered by broad membranous ligaments (Fig. 4, Nos. 29 and 60).

_Poupart’s ligament_ or _ligamentum Poupartii_, quite small in fowls, extends from the anterior lower rim of the ilium to the pelvic cavity, and is inserted at the bottom of the acetabulum.

Another broad ligament originates from the posterior rim of the ischium and is attached to the square surface of the first coccygeal vertebra.

The _ilio-pubic ligament_ extends from the pubic spine to the last rudimentary rib.

=Ligaments of the Hip-joint= (Fig. 25, _F_).—The hip-joint is made up of the ilium, ischium, pubis and femur and is a deep ball-and-socket joint. The cavity or acetabulum is called a cotyloid cavity.

The hip-joint is provided with three ligaments.

The _ligamentum capsulare femoris_ is attached around the rim of the cotyloid cavity and around the rim of the articular head of the femur (Fig. 25, No. _F_, 4).

The _ligamentum teres_, or _round ligament_, is a very short ligament which closes the hole at the floor of the cotyloid cavity, at which point it is attached. It is also attached to the head of the femur.

The _ligamentum ilio-sacrale_ strengthens the hip-joint capsule. It passes from the lower anterior rim of the os ilii, extending over the capsule to the neck of the femur to which it is attached.

=The Ligaments of the Knee-joint= (Figs. 16 and 17).—The knee-joint is made up of the femur, patella, tibia and fibula, and is provided with the following ligaments:

The _ligamentum extero-laterale genu_ is a strong ligament extending from the condylus externus femoris, or external femoral condyle to the outer surface of the head of the fibula, or capitulum fibulæ. From this head there passes inward, a strong ligament to a point between the femur and fibula (Fig. 25, No. _D_, 4).

FIG. 16.—Ligaments and muscles of the hind extremity.

_A._ A transverse section through the tibial or tarsal cartilage,
front view. 1, Gastrocnemius tendon. 2, Flexor perforatus annularis
primus pedis. 3, Flexor perforans digitorum profundus. 4, Flexor
perforatus indicis secundi pedis. 5, Extensor longus hallucis. 6,
The articular surface. 7, Ligamentum capsulare ossis tarsi. 8,
Flexor perforatus medius secundus pedis. 9, Flexor perforatus
indicis secundus pedis. 10, Tendons of the extensor muscles.

_B._ Knee-joint. Inside view of femoro-tibial articulation. 1,
Anterior ligamentum cruciatum. 2, Internal ligamentum laterale genu.
3, Anterior patellar ligament. 4, Patella. 5, Distal end of femur.
6, Proximal end of tibia. 7, Location of meniscus or pad of
fibrocartilage.

_C._ Anterior view of tibio-tarsal articulation. 1, Distal end of
tibia. 2, Its articular surface. 3, Ligamentum anticum. 4, Proximal
end of metacarpus. 6, Pad of fibrocartilage.

_D._ The dorsal surface of the coccyx. 1, The bilobate oil gland. 2,
Its duct. 3, Levator coccygis.

_E._ Inside view of pelvis and thigh. 1, Obturator internus. 2,
Ambiens. 3, Vastus internus. 4, Internal ligamentum laterale genu.
5, Tibialis anticus. 6, Loop through which the tibialis anticus
passes. 7, Adductors of the thigh. 8, Loop for the extensor tendon.
]

The _ligamentum intero-laterale genu_ extends from the outer surface of the internal condyle of the tibia, or condylus internus tibiæ. It gives off a thin ligamentous slip which enters the joint and is attached to the inner half-moon shaped pad of fibrous cartilage, or meniscus, which it draws backward by the flexion of the knee (Fig. 16, No. _B_, 2).

The _ligamentum popliteum_ arises from the fossa poplitea of the distal extremity of the femur and extends downward to the posterior rim of the head of the tibia.

The _anterior ligamentum cruciatum genu_ originates from the fossa poplitea and extends outward antero-laterally to the rim of the head of the tibia (Fig. 25, No. 6).

The _posterior ligamentum cruciatum genu_ is a short, strong ligament which originates from the cavity of the internal condyle of the femur, or condylus internus femoris, and inserts into the internal glenoid cavity of the tibia (Fig. 25, No. 1) or cavitas glenoidalis interna.

The meniscus of the femoro-tibial articulation is divided into four parts, as follows: first, the _internal adhesio cornu antici cartilaginis lunatæ_; second, the _posterior adhesio cornu antici cartilaginis lunatæ_; third, the _external cornu cartilaginis lunatæ_; fourth, the _anterior cornu antici cartilaginis lunatæ_. The latter originates between the condyles and passes around the ligamentum cruciatum genu posticum (Fig. 16, No. _B_, 7).

The inner semi-lunar fibrous cartilage is well developed and is joined by two ligaments between the femoral and the tibial surfaces (Fig. 25, No. 1).

The external semi-lunar cartilage lies in a cavity between the external femoral condyle and the head of the fibula (Fig. 25, No. 2).

The fibrous cartilages are bound posteriorly by a ligament, and by a second ligament to the head of the fibula, or capitulum fibulæ. Both pads of fibrous cartilage are connected by a transverse ligament called the _ligamentum transversale commune_ (Fig. 25, No. 5).

The patella is provided with several ligaments, as follows:

The _anterior patellar ligament_, broad, strong, and irregular in thickness, extends from the inferior margin of the patella to the rim of the second tibial crest (Fig. 16, No. _B_, 3).

The _ligamentum capsulare capituli fibulæ_ is spread out between the head of the fibula, or capitulum fibulæ, and the superficies glenoidalis peronea tibiæ.

FIG. 17.—Muscles and tendons of the head and posterior extremity.

_A._ Section of neck with superficial muscles removed. 1,
Obliquo-transversales. 2, Interspinales. 3, Intertransversales. 4,
Interarticulares.

_B._ Head showing muscles. 1, Beak. 2, Nostril. 3, Tongue. 4,
Sublingual salivary gland. 5, Pterygoideus. 6, Stylo-hyoideus. 7,
Temporal. 8, Flexor capitis inferior. 9, Rectus capitis lateralis.
10, Rectus capitis posticus major. 11, Trachelo-mastoideus. 12, Eye.
13, Mylo-hyoideus. 14, Genio-hyoideus. 15, Biventer maxilla. 16,
Digastricus. 17, Rectus capitis anterior minor.

_C._ Foot of hen showing tendons. 1, Flexor perforans digitorum
profundus. 2, Flexor perforatus medius primus pedis. 3, Sheath at
joint through which tendon passes. 4, Flexor perforatus indicis
primus pedis. 5, Flexor perforatus medius secundus pedis. 6, Flexor
perforatus annularis primus pedis. 7, Flexor longus hallucis.

_D._ Outside view of leg of hen. 1, Biceps flexor cruris. 2,
Semitendinosus. 3, Loop through which biceps flexor cruris passes.
4, Tibialis anticus. 5, Flexor perforatus indicis secundus pedis. 6,
Flexor perforatus medius primus pedis. 7, Gastrocnemius. 8, Flexor
perforatus annularis primus pedis. 9, Flexor perforatus medius
secundus pedis. 10, Extensor longus hallucis.
]

The _ligamentum tibio-fibulare_ extends from the head of the fibula, or capitulum fibulæ, to the inner surface of the external crest, or crista externa tibiæ, of the tibia (Fig. 25, No. 3).

The _ligamentum interosseum_ is a delicate ligament located between the tibia and fibula (Fig. 25, No. 4) which very early becomes ossified.

=Ligaments of the Tibio-metatarsal Joint= (Fig. 16).—The tibio-tarsal joint is made up of the tibia and metatarsus.

The _ligamentum capsulare ossis tibio-metatarsi_ connects the tibia and the metatarsus and surrounds the joint (Fig. 16, Nos. _A_, 7 and _C_, 7).

The _ligamentum externum_, a long strong ligament, originates on the upper and outer surface of the external condyle, or condylus externus of the tibia and is attached to the upper rim of the os metatarsi (Fig. 23, No. 15).

The _ligamentum anticum_ is spread out between the fossa intercondyloidea of the tibia and the tuberculum ossis metatarsi of the proximal end of the metatarsus (Fig. 16, No. _C_, 3). Just posterior to this ligament, there is an interosseous ligament, the _ligamentum interosseum_.

A semi-lunar pad of fibrous cartilage, the _cartilago semi-lunaris_ is located between the outer distal extremity of the tibia and upper articular surface of the metatarsus (Fig. 16, No. _C_, 6). Its concave portion is directed anteriorly and receives an insertion from the ligamentum externum, or external ligament.

The tendon Achillis (Fig. 16, No. _A_, 1) may become ossified.

=Ligaments of the Toes= (Fig. 16).—In addition to the capsular ligaments, which all true joints have, we find the following in connection with the toes:

The _ligamentum superius_ and the _ligamentum inferius_ connect the second toe with the great toe, or hallux.

The _ligamentum laterale externum_ and the _ligamentum laterale internum_ unite the bases of the second, third and fourth toes to the lateral faces of the trochleas of the inferior extremity of the metatarsus.

The bases of the toes are held together by the _ligamenta transversa_. All the rest of the toes are held together by the _ligamenta capsularia digitorum pedis_ and by two lateral ligaments, namely: the _ligamentum laterale externum_ and the _ligamentum laterale internum_.

MYOLOGY

=Kinds and Structure of Muscles.=—Muscles are highly specialized structures which have the property of contractility when stimulated, and thus produce motion. Muscular tissue is sometimes called flesh. Two kinds of muscles are recognized; muscles of locomotion and visceral muscles.

The muscles of locomotion may be in masses of different shape attached to the skin, the _dermal_, or to the skin and skeletal structure, the _dermo-osseous_, or from one bone to another, the _skeletal_. The visceral muscles form sheets and make up a portion of the wall of many of the hollow organs, such as the intestines, the stomach, the gizzard, the esophagus, and the blood-vessels. A special type of muscle forms the heart.

When classified with reference to structure, muscular tissue is divided into three types, as follows: voluntary-striated, involuntary, and involuntary-striated. The microscopic examination of each of these types of muscle shows it to be made up of fibers, these fibers to be made up of muscle cells, the muscle cell to be inclosed in a delicate tubular sheath, or membrane, called the _sarcolemma_. This membrane, tough and elastic, isolates each fiber. The bundles of fibers, called _fasciculi_, are surrounded by a fibrous sheath, which is called the _perimysium internum_; and the entire muscle has likewise an investing sheath of connective tissue, called the _perimysium externum_. The muscular cells show a longitudinal striation marking the fibrillæ, and they also show a cross striation. Nuclei are found just beneath the covering, or sarcolemma, in the striated muscle cell (Fig. 77, No. 2). In the involuntary and in the involuntary-striated muscle cell, the nuclei are centrally located.

The _voluntary-striated muscles_ consist of cylindrical fibers and with a few exceptions, are under the control of the will. A muscle of this type, the regular skeletal form, usually has at each extremity a fibrous structure, called a tendon, by means of which it is attached to the bones. The intermediate fleshy portion of the muscle, in case of considerable bulk, is called the belly of the muscle.

The _involuntary_, _non-striated_, or _smooth muscle_, cells are spindle-shaped, long, and pale in color (Fig. 77, No. 1). The cells lie end to end forming fibers. These fibers do not terminate in tendons, but are arranged in sheets and aid in forming the walls of the digestive tract, to which they give the power of contraction and expansion.

_Involuntary-striated_, or _heart muscle_ (Fig. 77, No. 4), occupies an intermediate position between the two muscles just described. It is composed of cells which branch, are somewhat rectangular. They possess both longitudinal and transverse striation. Among the fibers is found a small amount of connective tissue, as in the former types of muscle, which gives support to the blood-vessels and nerves.

=Fascia.=—The term fascia is applied to membranous expansions, differing materially in strength, texture, and relations. Fascia is composed of loosely arranged white fibrous connective tissue. At least two layers may usually be distinguished, the superficial fascia and the deep fascia.

Below the skin is the _superficial fascia_, which forms a continuous covering over the whole body and serves to attach the skin to the underlying structure.

The _deep fascia_ more densely constructed, may be attached to the skeleton, ligaments, and tendons.

When the fascia spreads out, becomes denser, and acts as a continuation of a muscle, it is called an aponeurosis.

=The Muscular Nomenclature.=—In the fowl there are 162 muscles, single or in pairs. These muscles are named from their location, as the lingualis; others from their attachments, as the dermo-temporalis; some from their form, as the rhomboideus; others from their use, as the flexor or extensor; and still others from their direction, as the transversus.

THE DERMAL MUSCLES

Birds are provided with a system of delicate muscles divided into numerous fasciculi, which harmoniously act upon the feather quills and collectively agitate the plumage. These are the dermal muscles. This group is divided into two subgroups: the true dermal muscles, that is, those that have their origin and insertion to the under surface of the skin; and the dermo-osseous, those that originate on the surface of some bone and insert to the inner surface of the skin.

TRUE DERMAL MUSCLES

Dermo-frontalis
Dermo-dorsalis
Dermo-tensor patagii
Dermo-humeralis
Dermo-pectoralis

=Dermo-frontalis.=[3] _Location._—This muscle is somewhat rudimentary and may be entirely absent. It is located in the frontal region and is about 2 or 3 centimeters long and not so wide.

Footnote 3:

The classification of Shufeldt is used.

_Origin and Insertion._—Closely attached to the skin.

_Shape._—Flat and rather rectangular.

_Relations._—Superiorly with the skin and inferiorly with the frontal bones.

_Action._—By contraction the feathers on the top of the head lie flat. Those above the eyes are elevated.

=Dermo-dorsalis.= _Location._—In the median line of the neck and back.

_Origin and Insertion._—Adhering closely to the skin, it generally becomes lost at the occiput; it is most highly developed in the mid-cervical region, and it gradually disappears over the caudal region.

_Shape._—Delicate and ribbon-shaped.

_Relations._—Superiorly it is attached to the skin. Fat sometimes surrounds the muscle.

_Action._—By contraction it raises the feathers along the superior part of the neck and dorsal region.

=Dermo-tensor Patagii.= _Location._—Between the root of the neck and top of the shoulder.

_Origin and Insertion._—Attached to the skin in the region of the anterior part of the root of the neck, some fibers passing obliquely upward and blend with fibers of the dermo-temporalis. It blends, by a slender tendon, with that of the tensor patagii longus.

_Shape._—A bundle of muscular fibers later becomes thin, delicate, and triangular in shape.

_Relations._—Externally to the skin.

_Action._—Auxiliary to the tensor patagii longus. A tensor of this region.

The patagii are associated with the wing fold of skin which fills the angle between the arm and forearm. This fold contains elastic tissue and muscle.

=Dermo-humeralis.= _Location._—Lateral thoracic region.

_Origin and Insertion._—Fan-like delicate fibers from the skin in the abdominal integument, contracting into a long narrow fasciculus of fibers, again spreading out in fan-shape to be inserted to the tendon of the pectoralis major, just below its insertion.

_Shape._—Triangular, fan-shape.

_Relations._—Superiorly with the skin.

_Action._—Controls the skin in this region. The anterior end being fixed, the muscles are raised; and the posterior end acting as the fixed point, the feathers are caused to lie close to the body.

=Dermo-pectoralis.= _Location._—On each side of the chest, lying in a longitudinal manner.

_Origin and Insertion._—Attached to the skin on either side of the thorax corresponding to the dermo-dorsalis. Anteriorly it disappears over the region of the origin of the cleido-trachealis, and posteriorly just behind the tips of the post-pubic parts of the pelvis.

_Shape._—Thin, delicate.

_Relations._—Superiorly with the skin.

_Action._—The anterior part acting as the fixed point, the feathers of the chest are raised; and the posterior end acting as the fixed point, the feathers are made to lie flat.

THE DERMO-OSSEOUS MUSCLES

Dermo-temporalis
Platysma myoides
Dermo-cleido dorsalis
Cleido-trachealis
Dermo-spinalis
Dermo-iliacus
Dermo-ulnaris

=Dermo-temporalis= (Fig. 18, No. 1). _Location._—From the temporal region down the side of the neck to the anterior part of the thoracic region.

_Origin._—By a broad tendinous attachment from a small depression above and anterior to the temporal fossa. From here the fibers pass upward and backward and then downward.

_Insertion._—A few fibers blend with those of the cleido-trachealis. The fibers are then lost upon the skin in front and opposite the shoulder-joint. Some of the fibers blend with those of the dermo-tensor patagii.

_Shape._—Long, flat, and ribbon-shaped. The lower portion consists of delicate fibers.

_Relations._—Superior to the temporal muscle and sphenotic process. Superior to the cleido-trachealis and inferiorly to the shoulder-joint. The superior portion touches the skin throughout its entire length.

_Action._—A tensor of the lateral cervical integument. It is an auxiliary to the tensor patagii.

=Platysma Myoides.= _Location._—The inferior portion of the throat.

_Origin._—From the lower margin of the rami of the jaw. Just inferior to the attachment of the masseter.

FIG. 18.—Muscles of the upper neck region, 1, Dermo-temporalis. 2,
Cornu of the os hyoideum. 3, Carotid artery. 4, Jugular vein. 5,
Pneumogastric nerve. 6, Esophagus. 7, Trachea.
]

_Insertion._—From the point of origin it spreads out into a thin fan-like layer and meets its fellow in the median raphe. It is attached to the skin in this region.

_Shape._—A very thin fan-shaped muscle.

_Relations._—Closely adherent to the skin.

_Action._—Assists in supporting the lingual apparatus and superior larynx. Compresses and elevates the part.

=Dermo-cleido Dorsalis.= _Location._—Anterior shoulder region.

_Origin._—From the upper mesial part of the clavicular bone.

_Insertion._—Three fasciculi forming a fan-like arrangement attached to the skin in the shoulder-joint and scapular region. The extremities of the fasciculi may meet in the median line of the dorsal region and merge with the dermo-dorsalis.

_Shape._—Three fasciculi forming a fan-shaped radiation.

_Relations._—Superiorly with the skin. Inferiorly with the shoulder-joint.

_Action._—Contracting with the origin as the fixed point, they brace the skin over the forepart of the back. With the integumental attachment as the fixed point, they aid in the act of respiration.

=Cleido-trachealis.= _Location._—Extending from the shoulder to the superior laryngeal region.

_Origin._—From a small area on the antero-inner part of the middle of the arm of the furcula.

_Insertion._—The fibers pass upward and become flattened and attached to the skin and dermo-temporalis muscle. They touch each other on the anterior border of the superior larynx, the trachea, and the skin over these parts.

_Shape._—A slender bundle of muscles.

_Relations._—Superiorly the skin, and internally the larynx and the trachea.

_Action._—Controls the skin region of this part of the neck.

=Dermo-spinalis.= _Location._—In the region of the shoulder.

_Origin._—In an attenuated fascia from the crest of the neural spines of the first, the second, and the third dorsal vertebræ.

_Insertion._—To the skin in a broad pale stratum, over the scapular region.

_Shape._—Thin, pale, and very delicate.

_Relations._—Superiorly with the skin, and inferiorly with the shoulder.

_Action._—Controls the skin of the region.

=Dermo-iliacus.= _Location._—Along the back on either side of the spine.

_Origin._—From the inner angle of the marginal portion of the antero-dorsal border of the ilium.

_Insertion._—Passing forward as a delicate band it spreads out and becomes lost in the skin of the shoulder region.

_Shape._—Thin, delicate, and ribbon-shaped.

_Relations._—Superiorly with the skin.

_Action._—If the posterior end is fixed, it will cause the feathers to lie close to the skin. Its action would then be opposite to the dermo-dorsalis.

=Dermo-ulnaris.= _Location._—Outer surface of the anterior upper costal and the posterior humeral region.

_Origin._—By a thin fascia from the outer part of the third and the fourth true ribs at the base of their epineural appendages. Also from the fascia between them.

_Insertion._—The fibers pass forward and upward as a thick muscular bundle and is loosely attached to the skin at a point just back of the humerus. The tendon later becomes spread out and attached to the fascia as far as the elbow-joint. It covers the olecranon of the ulna.

_Shape._—At first rather thick, fascicular-like; later becomes tendinous; and at its attachment it becomes spread out over the olecranon.

_Relation._—Inferiorly with the ribs and humerus, and externally with the skin.

_Action._—A depressor of the humeral region.

THE SKELETAL MUSCLES

THE MUSCLES OF THE HEAD

Temporal
Masseter
Biventer maxillæ
Entotympanicus
Pterygoideus internus
Pterygoideus externus
Digastricus

=Temporal= (Fig. 19, No. 4). _Location._—Occupies the temporal fossa.

_Origin._—From the mesian line of the sphenotic process, and the adjacent wall of the orbit.

_Insertion._—The fibers passing downward and forward blend with the fibers of the masseter. Inferiorly it inserts by a tendon to the coranoid process upon the superior ramal margin of the mandible.

_Shape._—Fan-shaped with broad portion uppermost.

_Relations._—It occupies the temporal fossa. It is related superiorly with the dermo-temporalis and skin. Inferiorly, with the biventer maxillæ and the masseter.

_Action._—It aids in closing the jaw.

=Masseter= (Fig. 19, No. 1). _Location._—Occupies the supero-lateral portion of the surface of the lower jaw.

_Origin._—In two portions: the first, by a broad and thin tendon from the entire length of the bony ridge above the external auditory meatus, from the squamosal process, and from the outer portion of the quadrate bone; the second, from the side and under border of the zygoma.

_Insertion._—The first portion: The fibers pass downward and forward beneath the zygoma; a few of the fibers blend with those of the temporal; one tendon inserts to a small tubercle on the upper border of the jaw behind the coronoid process, and by fleshy insertion to the outer side of the ramus of the lower jaw, quite as far forward as the horny portion of the beak. The second portion: by a small tendon to the mandible on its upper border immediately in front of the articular portion.

_Shape._—Flat, and elongate. Somewhat fleshy.

_Relations._—Superiorly with the temporal, and inferiorly with the biventer maxillæ and stylo-hyoideus. Externally with the skin, and internally with the jaw bone.

_Action._—Aids in closing the jaw.

=Biventer Maxillæ= (Fig. 19, No. 3). _Location._—Covers the outer posterior portion of the mandible.

_Origin._—It arises in two portions: The first, from a ridge bounding the posterior part of the auditory canal; the second, from a depression of the mesial side. These two parts blend and extend downward and forward.

_Insertion._—To the posterior part of the articular end of the mandible.

_Shape._—A curved fleshy mass.

_Relations._—Superiorly with the temporal and stylo-hyoideus. Posteriorly with the digastricus and genio-hyoideus. Internally with the jaw bone, and externally with the skin.

_Action._—It aids in opening the jaw.

=Entotympanic.= _Location._—Posterior to the pterygoid.

_Origin._—From the side of the basi-sphenoid and from the base of the rostrum immediately beyond it.

_Insertion._—The fibers pass downward and forward, and insert by a double tendinous slip. One slip inserts to a spine-like process on the upper side of the pterygoid, and the other to the quadrato-pterygoidean articulation.

_Shape._—Spindle-shaped.

_Relations._—Anteriorly with the pterygoid. Internally and posteriorly with the basi-sphenoid. Externally with the pterygoideus internus.

_Action._—Aids in raising the upper mandible by pulling forward the quadratus and pterygoidean against the palatines.

=Pterygoideus Internus= (Fig. 17, No. _B_, 5). (Synonym.—Pterygoideus medialis.[4])

Footnote 4:

According to international veterinary nomenclature.

_Location._—A muscular mass at the roof of the mouth.

_Origin._—From the major part of the surface of the palatine bone and the distal head and shaft of the pterygoid and the sphenoidal projection.

_Insertion._—By a tendon to the antero-internal part of the articular part of the mandible.

_Shape._—Fusiform with a thick fleshy belly.

_Relations._—Superiorly with the palatine, the pterygoid, and the sphenoid bones. Inferiorly with the skin.

_Action._—It aids in closing the jaw.

=Pterygoideus Externus.= (Synonym.—Pterygoideus lateralis.)

_Location._—Supero-external to the pterygoideus internus.

_Origin._—From the outer part of the extremity of the orbital process of the quadrate.

_Insertion._—The fibers pass downward, outward and forward and are inserted to the inner part of the mandibular ramus.

_Shape._—A small round bundle.

_Relations._—Inferiorly with the pterygoideus internus. Externally with the inferior maxilla.

_Action._—Aids in closing the jaw.

=Digastricus= (Fig. 17, No. _B_, 16). _Location._—Extends from the basi-temporal to the side of the neck.

_Origin._—From the external lateral angle of the basi-temporal.

_Insertion._—Opposite the angle of the jaw the fibers spread out in fan-like arrangement. The muscle meets its fellow of the opposite side; extends longitudinally over the superior larynx, for some distance down the neck.

_Shape._—Thin and ribbon-shaped.

_Relations._—Externally to the platysma myoides. The anterior fasciculi blend with those of the mylo-hyoideus; internally with the larynx at the upper part.

_Action._—To raise the trachea and hyoid apparatus against the pharynx.

THE MUSCLES OF THE TONGUE

Mylo-hyoideus
Stylo-hyoideus
Genio-hyoideus
Cerato-hyoideus
Sterno-hyoideus
Depressor-glossus
Cerato-glossus
Hyoideus transversus

=Mylo-hyoideus.= _Location._—The forepart of the inter-ramal space.

_Origin._—From the inner side of the lower jaw at a point just above the lower border and the inturned edge of the horny sheath of the beak.

_Insertion._—By aponeurosis to the under side of the hyoid, on the median line between the first and the second basi-branchial.

_Shape._—Thin, flat, and delicate.

_Relations._—Inferiorly with the skin. Thin and rather broad, it meets its fellow of the opposite side. Laterally with the rami of the jaw. Superiorly with the hyoid apparatus.

_Action._—Lifts the tongue upward against the roof of the mouth.

=Stylo-hyoideus= (Fig. 17, No. _B_, 6). _Location._—Supero-posterior to the hyoid apparatus.

_Origin._—From the outer portion of the articular enlargement of the lower jaw.

_Insertion._—By a tendon to the basi-branchial of the thyro-hyal.

_Shape._—A long transversely flattened fasciculus.

_Relations._—Supero-posterior part of the hyoid apparatus along side the genio-hyoideus and the cerato-hyoideus.

_Action._—Singly, pulls the tongue to one side; acting with its fellow, pulls the tongue upward.

=Genio-hyoideus= (Fig. 9, No. 7). _Location._—Supero-posterior to the hyoid apparatus.

_Origin._—From the anterior portion of the inner side of the lower jaw.

_Insertion._—To the middle of the outer side of the basi-branchial of the corner of the os hyoides which cornu it completely envelops.

_Shape._—A long, rather thick fasciculus.

_Relations._—With the stylo-hyoideus and cerato-hyoideus.

_Action._—Protrudes the tongue from the mouth.

=Cerato-hyoideus= (Fig. 9, No. 8). (Synonym.—Kerato-hyoideus.)

_Location._—Inferior to the hyoid apparatus.

_Origin._—By a delicate tendinous slip from the under side of the shaft of the basi-hyal element of the hyoid apparatus.

_Insertion._—To a small elevation on the under side of the anterior end of the glosso-hyal.

_Shape._—A small round muscular fasciculus becoming tendinous in its anterior half.

_Relations._—Superiorly with the hyoid apparatus.

_Action._—Singly, pulls the tongue to one side; acting with its fellow, depresses the tongue.

=Sterno-hyoideus.= _Location._—Inferior to the hyoid apparatus.

_Origin._—From the outer anterior surface of the thyroid bone of the superior larynx.

_Insertion._—To the anterior part of the basi-hyal.

_Shape._—At first broad and rather fleshy, becomes contracted and somewhat tendinous.

_Relations._—Inferior to the hyoid apparatus and superior larynx.

_Action._—When the larynx is fixed, acting alone deflects the tongue laterally; acting with its fellow, depresses the tongue. If the base of the tongue is fixed the two pull the larynx forward. Hence muscles of deglutition.

=Depressor-glossus.= _Location._—Superior to the basi-hyal.

_Origin._—From the under portion of the basi-hyal.

_Insertion._—To under part of the glosso-hyal.

_Shape._—Small, short.

_Relations._—Superiorly with the basi-hyal and glosso-hyal bones.

_Action._—Depresses the tip of the tongue and elevates the base.

=Cerato-glossus.= _Location._—On the upper portion of the cornu of the hyoid.

_Origin._—One-half of the surface of the first basi-branchial.

_Insertion._—To the upper side of the shaft of the cerato-branchial element of the hyoid apparatus.

_Shape._—A small muscular fasciculus.

_Relations._—Supero-laterally to the cerato-branchial element.

_Action._—Elevates the cornua of the hyoid arches and presses them against the skull.

=Hyoideus Transversus= (Fig. 9, No. 9 and 10). _Location._—Envelops the spur process of the euro-hyal.

_Origin and Insertion._—It extends from the inner side of one cornu to the spur process.

_Shape._—Thin, flat.

_Relations._—Posterior to the euro-hyal, which it envelops, and between the cornua of the os hyoides.

_Action._—Approximates the cornua of the os hyoides.

THE CERVICAL MUSCLES

Complexus
Rectus capitis anticus minor
Flexor capitis inferior
Rectus capitis posticus major
Biventer cervicis
Longus colli posticus
Obliquus colli
Longus colli anterior
Rectus capitis lateralis
Trachelo-mastoideus
Interspinales
Interarticulares
Obliquo-transversales
Intertransversales
Scalenus medius

=Complexus= (Fig. 19, No. 5). _Location._—Supero-lateral portion of the neck.

_Origin._—By three tendinous slips from the antero-lateral portion of the transverse process of the fourth, the fifth, and the sixth cervical vertebræ.

_Insertion._—The muscular fibers pass around the neck and meet their fellows in the median line in a fascia formation. The thin tendinous sheet inserts into the occiput just above the occipital ridge.

_Shape._—From point of origin this muscle expands into a broad sheet.

_Relations._—It overlies the muscles of the occipital region.

_Action._—It extends the head.

=Rectus Capitis Anticus Minor= (Fig. 19, No. 8). (Synonym.—Rectus capitis ventralis minor.)

_Location._—Infero-lateral portion of the neck.

_Origin._—From the apices of the hyapophyses of the second, the third, and the fourth cervical vertebræ.

_Insertion._—To the occiput just below the complexus.

_Shape._—A long and rather thick fasciculus.

_Relations._—Externally with the skin. The tendinous slips of origin pass between the flexor capitis inferior and longus colli anterior.

_Action._—Extends the head.

=Flexor Capitis Inferior= (Fig. 19, No. 7). _Location._—Antero-inferior part of the neck.

_Origin._—From the apices of the hyapophyses of the second, the third, and the fourth cervical vertebræ.

_Insertion._—To the triangular area on the basi-temporal of the base of the cranium.

_Shape._—At first tendinous, becomes somewhat fleshy as it passes forward.

FIG. 19.—Muscles of the head and neck. 1, Masseter muscle. 2,
Infraorbital sinus. 3, Biventer maxilla. 4, Temporalis. 5,
Complexus. 6, Rectus capitis posticus major. 7, Flexor capitis
inferior. 8, Rectus capitis anticus minor. 9, Biventer cervicis. 10,
Longus colli posticus. 11, Obliquus colli. 12, Intertransversales.
13, Longus colli anterior. 14, Lateral temporo-maxillary ligament.
15, Lateral ligament of the jaw. 16, Trachelo-mastoideus. 17, Rectus
capitis lateralis. 18, Scalenus medius. 19, Rhomboideus. 20,
Trapezius. 21, Location of scapula. 22, Supraspinatus. 23, Teres et
Infraspinatus.
]

_Relations._—Antero-inferior portion of the neck close to the rectus capitis anticus minor.

_Action._—Flexes the head upon the neck.

=Rectus Capitis Posticus Major= (Fig. 19, No. 6). (Synonym.—Rectus capitis dorsalis major.)

_Location._—Supero-lateral area on the anterior portion of the neck.

_Origin._—From the median anterior aspect of the second cervical vertebra, and the supero-anterior border of the neural canal.

_Insertion._—To the crescent-shaped area at the back of the skull.

_Shape._—Short, thick, fleshy bundle.

_Relations._—Superiorly with the complexus; inferiorly with the trachelo-mastoideus and the vertebræ.

_Action._—Singly, pulls the head to one side; acting with its fellow, extends the head.

=Biventer Cervicis= (Fig. 19, No. 9). _Location._—Occupies the superior part of the neck.

_Origin._—From the side of the neural spine of the first dorsal vertebra, and from the adjacent tendon of the longus colli posticus.

_Insertion._—To the occiput.

_Shape._—Tendinous in the middle with a more or less spindle-shaped belly at each end.

_Relations._—Superior to the longus colli posticus. It lies next to the skin.

_Action._—Extends the head on the neck and elevates the neck.

=Longus Colli Posticus= (Fig. 19, No. 10). (Synonym.—Longus colli dorsalis.)

_Location._—Occupies the superior part of the neck.

_Origin._—From the marginal edges of the summits of the neural spines of the first two dorsal vertebræ.

_Insertion._—To the transverse process of the axis, and superior part of the cervical vertebræ.

_Shape._—A long, somewhat narrow, flattened muscle, the inferior portion of which is divided into five or six fasciculi.

_Relations._—Superiorly with the biventer cervicis and inferiorly with the vertebræ.

_Action._—Raises the neck upward.

=Obliquus Colli= (Fig. 19, No. 11). _Location._—On the lateral side of the neck.

_Origin and Insertion._—The first of the seven fasciculi originates from the diapophysis of the eleventh cervical vertebra, winds obliquely over the tenth, and is inserted into the posterior margin of the postzygapophysis of the ninth vertebra. In its passage it receives the slip from the longus colli posticus. The next fasciculus originates from the transverse process of the tenth cervical vertebra, winds obliquely over the ninth vertebra, and is inserted to the postzygapophysis of the eighth vertebra. In its passage it also receives a fasciculus from the longus colli posticus. The next three fasciculi originate in a similar manner being attached to similar postzygapophyses and have slips extending forward which slips are inserted to the neural spines of the alternate vertebræ. The sixth fasciculus originates from the transverse process of the sixth vertebra, passing obliquely up the neck is inserted to the extremity of the diapophysis of the fourth vertebra, the outer extremity of the transverse process of the third vertebra. The seventh, or anterior, fasciculus originates from the transverse process of the fifth vertebra, and is inserted to the extremity of the diapophysis of the third vertebra.

_Shape._—Short, thick fasciculi.

_Relations._—Laterally with the vertebræ. Inferiorly with the intertransversales. Superiorly with the longus colli posticus, and externally with the skin.

_Action._—Flexes one vertebra on the other laterally.

=Longus Colli Anterior= (Fig. 19, No. 13). (Synonym.—Longus colli ventralis.)

_Location._—Occupies the anterior portion of the neck.

_Origin and Insertion._—This muscle is divided into a vertical portion, and a superior and an inferior oblique portion. The vertical portion originates from the hypophyses of the tenth to the fifteenth vertebra and is inserted by a tendon to the tubercle on the inferior portion of the atlas. Small, slender tendons are given off and insert to the apices of the parapophyses of the fourth to the tenth cervical vertebræ. There is more or less attachment to the bodies of the cervical vertebræ mentioned. The superior oblique portion originates from the diapophyses of the third, the fourth, the fifth cervical vertebræ and becoming tendinous is inserted to the tubercle on the inferior portion of the body of the atlas. The inferior oblique portion originates from the transverse processes of the fourth, the fifth, and the sixth cervical vertebræ. It is inserted by a slender tendon to the apex of the parapophysis of the third cervical vertebra.

_Shape._—A long fleshy muscle extending the entire length of the neck.

_Relations._—Inferiorly with the skin and superiorly with the cervical vertebræ.

_Action._—Pulls the neck downward.

=Rectus Capitis Lateralis= (Fig. 19, No. 17). _Location._—The infero-lateral anterior portion of the neck.

_Origin._—Originates tendinous from the diapophysis of the third, the fourth, and the fifth cervical vertebræ.

_Insertion._—Passes obliquely upward in front of the spinal column to the inner tubercle on the basal ridge of the basi-temporal bone, by a subcompressed tendon.

_Shape._—A somewhat thick fasciculus.

_Relations._—Superiorly with the trachelo-mastoideus, inferiorly with the longus colli anterior, and externally with the skin.