Chapter VI: Bones of the Pelvic Extremities (2)

_Origin_ on the ligament which connects the zygomatic process of the frontal with the frontal process of the malar. The fibres form a thin band about 7 millimeters wide which passes craniad, closely united to the inner surface of the frontoscutularis. At the caudal edge of the zygomaticus (_d_) the muscle is interrupted by a short tendinous interval; the fibres then continue to their insertion on the tip of the antitragus.

_Relations_.--Outer surface with the frontoscutularis, the zygomaticus (_d_), and the integument. Inner surface with the temporal muscle and M. antitragicus (_n_).

_Action._--Pulls the ear craniodorsad.

* * * * *

The remainder of the muscles of the ear, which, with the exception of the tragicus lateralis, merely interconnect the cartilages of the external ear or parts of these cartilages, are described in connection with the account of the Auditory Organ.

* * * * *

Owing to the presence of the fibrous pad to which the whiskers are attached, the facial muscles between the eye and the mouth differ in the cat in some respects from those of related animals. This fibrous pad interrupts the muscles, frequently breaking muscles which are elsewhere single into two.

=M. zygomaticus minor=, or malaris (Fig. 64, _e_).--This muscle is not always present; when it exists it forms a very thin flat band of fibres passing from the ventral side of the eye toward the angle of the mouth.

_Origin_ among the fibres of the orbicularis oculi (_s_) in the lower eyelid. The fibres pass ventrad; the insertion varies. In some specimens the insertion is among the fibres of the orbicularis oris (_i_), at the angle of the mouth, beneath the zygomaticus (_d_). In other cases this muscle is said to be inserted into the pad on which the whiskers rest.

_Relations._--Outer surface with the integument and near its insertion with the zygomaticus major (_d_). Inner surface with the malar bone and the masseter muscle.

_Action._--Pulls the angle of the mouth (or the whiskers) dorsad.

=M. orbicularis oris= (Fig. 64, _i_).--This forms a very thin layer of subcutaneous concentric fibres which surround the mouth, that of the upper lip being thicker than that of the lower lip. The part of the muscle in the lower lip has its fibres intermingled with those of the platysma (_a′_). In the median line the fibres of the upper lip are interrupted by a raphe, and caudad of this are intermingled with those of the caninus.

=M. quadratus labii superioris= (Fig. 63, _p_ and _q_; Fig. 64, _f_ and _g_).--This is a complex of muscle-fibres attached chiefly to the fibrous pad on which the whiskers rest. In it two parts can be distinguished more or less completely.

(1) =M. levator labii superioris alæque nasi= (Fig. 63, _p_; Fig. 64, _g_) on the sides of the nose. This arises (_a_) as a continuation of the frontal portion of the epicranius, and (_b_) in a small bundle (Fig. 63, _p_) from near the dorsal end of the frontal process of the maxillary bone, in common with the next. The two slips thus formed unite craniad and are inserted partly into the integument on the outer side of the wing of the nose, partly into the skin of the upper lip, lateroventrad of the nose, and partly into the pad on which the whiskers are located, in connection with the next.

(2) The =angular= head (=caput angulare=), or =levator labii superioris proprius= (Fig. 63, _q_; Fig. 64, _f_) is much larger than the last. It takes origin from a small tubercle at the cranial border of the orbit, close to the origin of the orbicularis oculi. The fibres diverge from their origin to their insertion among the whiskers and in the fibrous pad on which the whiskers rest.

_Action._--Erects the whiskers and raises the upper lip.

=M. caninus= or =levator anguli oris= (Fig. 64, _f′_).

_Origin_ in a depression on the lateral surface of the maxillary bone, just craniad of the last premolar tooth. The fibres pass craniad, diverging, toward the whiskers, and have their insertion into the pad of tissue on which the whiskers rest.

_Action._--Retracts the whiskers and raises the upper lip.

=M. buccinator.=--A thin muscle against the mucous membrane of the upper lip, partly united with the orbicularis oris and lying beneath M. caninus.

_Origin_ on the outer surface of the superior maxillary bone in the depression between the infraorbital foramen and the first premolar tooth. The fibres pass ventrad, diverging, and mingle with those of the deep part of the orbicularis oris.

_Relations._--Outer surface with the caninus and with the orbicularis oris. Inner surface with the mucous membrane of the upper lip.

_Action._--Raises the upper lip.

=M. myrtiformis= (probably corresponds to a part of the human M. nasalis) (Fig. 64, _h_).--A thin sheet of muscle-fibres lying craniad of the levator labii superioris alæque nasi and passing from the whiskers to the nose and upper lip. It is distinguishable from the alæque nasi by the direction of the fibres.

_Origin_ from the pad upon which the whiskers rest. The fibres diverge and have their

_Insertion_ upon the wing of the nose and into the skin of the upper lip near the median line.

_Action._--Dilator of the nares and elevator of the upper lip.

=M. “moustachier”= (Str.-D.) (probably corresponds to one of the Mm. incisivi).--It lies on the upper lip near the median line.

_Origin_ from the outer surface of the premaxilla near the suture along the ventral border of the narial opening. The fibres diverge and pass caudad into the upper lip within the superficial fibres of the orbicularis oris.

_Insertion._--The skin of the upper lip just craniad of the whiskers. Some of the fibres pass into the pad on which the whiskers rest.

_Action._--It carries the lip craniad.

=M. quadratus labii inferioris.=--A thin flat band extending almost the length of the lower lip.

_Origin_ from the alveolar border of the mandible, between the molar tooth and the canine. The fibres pass dorsad into the lower lip, where they intermingle with those of the orbicularis oris. The muscle is perhaps not constant.

_Action._--Depressor of the lower lip.

Sometimes a few fibres arising from the cranial portion of the alveolar border of the mandibula pass mediad, seeming to join corresponding fibres from the opposite side. Such fibres would constitute a M. transversus menti.

B. DEEP MUSCLES OF THE HEAD.

(_a_) _Muscles of Mastication._

=M. digastricus= (Fig. 65, _b_).--The digastric is a thick prismatic muscle lying mediad of the angle of the lower jaw, connecting it with the base of the skull.

_Origin_ by fleshy fibres from the outer surface of the jugular process of the occipital bone, and by a thin tendon from the tip of the mastoid process and from the ridge between the mastoid and the jugular processes. The muscle passes craniad, becoming at the same time broader and more voluminous.

_Insertion._--The ventral border of the mandible craniad of the caudal border of the molar tooth. The insertion area extends slightly onto both surfaces of the bone and is triangular, with its apex craniad.

_Relations._--Outer (ventral) surface with the following, beginning at the caudal end: the rectus capitis lateralis, the cleidomastoid (_h_), the submaxillary gland (2), the stylohyoid (_d_), a large lymph-gland (3), and the integument. Inner (dorsal) surface with the jugulohyoid, the tympanic bulla, the masseter (_a_), the hyoglossus, and the mylohyoid (_c_).

_Action._--Depressor of the lower jaw.

=M. masseter= (Figs. 65 and 66, _a_).--The masseter forms the projecting mass so prominent in the cat behind and below the eye. Its outer surface is covered by a strong aponeurosis. The muscle is divided into three layers which are distinct as to origin, insertion, and direction of fibres, but which are otherwise not distinct.

The =superficial layer= takes

_Origin_ by the superficial aponeurosis from the ridge which runs lengthwise of the outer surface of the malar bone, and by fleshy fibres from the surface of the malar bone ventrad of this ridge. The fibres pass obliquely caudad to their insertion.

_Insertion._--The caudal half of the lateral margin of the ventral border of the mandible, by a sheet of fascia which lies on the inner surface of the muscle. The superficial fibres curve ventrad of the mandible and are inserted into a tendinous intersection between this muscle and the internal pterygoid (Fig. 66, _c_).

The =middle layer= takes

_Origin_ from the ventral border of the malar bone, from opposite the molar tooth to within three millimeters of the mandibular fossa. The fibres pass ventrad and have their

_Insertion_ into the mandible at the ventral border of the external coronoid fossa by means of the aponeurosis which covers the inner surface of the muscle.

The left side shows the first layer of muscles beneath the skin and
skin-muscles; the right side shows the second layer, except in the
head region. _a_, M. masseter; _b_, M. digastricus; _c_, M.
mylohyoideus; _d_, M. stylohyoideus; _e_, M. sternohyoideus; _f_, M.
thyreohyoideus; _g_, M. sternomastoideus; _g′_, M. sternothyreoideus;
_h_, M. cleidomastoideus; _i_, M. levator scapulæ ventralis; _j_, M.
clavotrapezius; _k_, M. clavobrachialis; _l_, M. pectoralis major;
_m_, M. pectoantibrachialis; _n_, part of M. scalenus; _o_, M.
pectoralis minor; _p_, M. xiphihumeralis; _q_, M. latissimus dorsi;
_r_, M. epitrochlearis; _s_, caput longum of M. triceps brachii; _t_,
M. biceps brachii; _t′_, bicipital arch; _u_, M. acromiodeltoideus;
_v_, M. brachialis. 1, parotid gland; 2, submaxillary gland; 3,
lymphatic glands; 4, external ear; 5, external jugular vein; 6,
manubrium; 7, first rib; 8, common carotid artery; 9, molar gland.]

The =deep layer= takes

_Origin_ by a strong tendon from the ventral border of the zygoma just craniad of the mandibular fossa. The fibres pass cranioventrad, diverge and have their

_Insertion_ into the external coronoid fossa.

_Relations._--Outer surface with the following, beginning at the caudal border: the external ear, the parotid gland (Fig. 65, 1), the platysma, the submentalis, the zygomaticus (major), the zygomaticus minor. Ventral border with a lymph gland caudad of the angle of the mouth (Fig. 65, 3), and the digastric muscle (_b_). Inner surface with the bones.

_Action._--A very powerful elevator of the lower jaw.

=M. temporalis= (Fig. 63, _n_).--The temporal muscle is the great mass taking origin from the temporal fossa and having its insertion on both surfaces and both borders of the coronoid process of the mandible. It may be divided into two layers, deep and superficial.

The =superficial layer=. The temporal fascia stretches over the temporal fossa, being attached to its borders; that is, to the sagittal and lambdoidal crests, to the curved ridge which connects the sagittal crest with the zygomatic process of the frontal bone, to the caudal border of this process, to the caudal border of the malar bone, to the caudal border of the ligament connecting the malar bone and the zygomatic process of the frontal, and to the dorsal border of the zygomatic process of the temporal bone and its dorsal root. The craniolateral part of this fascia is much stronger than the remainder.

The muscle-fibres take origin from the strong craniolateral part of the inner surface of the temporal fascia, from the groove on the temporal bone dorsad of the dorsal root of its zygomatic process, from the whole inner surface of this process and of the zygomatic process of the malar bone, and sometimes also from that part of the frontal bone which lies within the temporal fossa.

_Insertion.-_-The outer surface of the coronoid process of the mandible dorsad of the coronoid fossa, and both borders of the coronoid process. The cranial fibres may be inserted craniad of the coronoid process onto the aponeurosis covering the deep portion of the muscle. The caudal part of this portion is more or less distinct and is sometimes described as a separate head.

The =deep portion=.

_Origin_ by fleshy fibres from the whole surface of the temporal fossa, except in cases where the cranial part of the fossa is occupied by the superficial portion. The fibres converge toward the coronoid process, and the ventral third of the outer surface is covered by strong fascia.

_Insertion._--The whole inner surface of the coronoid process of the mandible.

_Relations._--Outer surface with the external ear, the ear-muscles (Fig. 63), the epicranius (Fig. 63, _h_), the corrugatores supercilii lateralis (_d_) and medialis (_b_). Inner surface with the skull, the pterygoideus externus (Fig. 66, _b_), and the structures within the orbit.

_Action._--Elevator of the lower jaw.

=M. pterygoideus externus= (Fig. 66, _b_).--This lies on the medial side of the mandible, ventrad of the ventral portion of the temporal.

_Origin._--The external pterygoid fossa (Fig. 40, _h_), which lies on the lateral surface of the perpendicular plate of the palatine bone, and on the surface of the pterygoid process of the sphenoid bone dorsad of the internal pterygoid fossa. The fossa extends from the foramen rotundum to the sphenopalatine foramen. The muscle passes with parallel fibres laterad, ventrad, and caudad and has its

_Insertion_ by a strong flat tendon into the medial surface of the mandible near its ventral border between the opening of the mandibular canal and the base of the angular process.

_Relations._--Ventral surface with the masseter (_a_), the digastric, and the soft palate with its muscles. Dorsal surface with the temporal, and near its origin with the muscles of the eye, and other structures in the orbit.

_Action._--Elevator of the lower jaw.

=M. pterygoideus internus= (Fig. 66, _c_).--This lies caudad of the pterygoideus externus, nearly parallel to it, and is connected with it at its lateral end.

_Origin_ from the whole surface of the internal pterygoid fossa (Fig. 40, _s_).

_Insertion_ by fleshy fibres into the ventral surface of the external pterygoid and its tendon, into the medial surface of the angular process of the mandible and caudad of the angular process for about one centimeter into a fascia common to it and the masseter muscle, and into the stylomandibular ligament.

The tongue and other structures forming the floor of the mouth have
been removed, showing the roof of the mouth. On the right side the
masseter and pterygoideus internus have been removed, _a_, _a′_, M.
masseter; _b_, M. pterygoideus externus; _c_, M. pterygoideus
internus; _d_, _d′_, M. tensor veli palatini; _e_, _e′_, M. levator
veli palatini; _f_, M. constrictor pharyngis superior. 1, aponeurosis
of the velum palatinum; 2, ridges formed by the palatines and
pterygoid portions of the sphenoid; 3, hamular processes; 4, free
caudal border of the velum palatinum; 5, bulla tympani.]

_Relations._--Ventral surface with the styloglossus and the soft palate. Dorsal surface with the bulla tympani (5) and base of the skull. Cranial surface with the pterygoideus externus (_b_), with which it is partly united.

_Action._--Assists the pterygoideus externus.

(_b_) _Muscles of the Hyoid Bone._

=M. stylohyoideus= (Fig. 65, _d_).--The stylohyoid is a ribbon-like muscle about three millimeters wide. It lies on the superficial surface of the digastric, caudad and ventrad of the angle of the jaw.

_Origin_ by fleshy fibres from the outer surface of the stylohyal bone near its middle. The muscle curves over the outer surface of the digastric (_b_), and ends about one centimeter from the middle line in a slender flat tendon.

_Insertion_ into the middle of the ventral surface of the body of the hyoid bone. Some of the fibres of the mylohyoid (_c_) are inserted into its tendon.

_Relations._--Outer surface with the submaxillary gland (2) and the submentalis muscle. Inner surface with the digastric (_b_), the hyoglossus (Fig. 67, _h_), and the geniohyoid (Fig. 67, _g_).

_Action._--Raises the hyoid.

=M. geniohyoideus= (Fig. 67, _g_).--The geniohyoid is a long slender muscle which lies next to the median line between the symphysis menti and the hyoid bone, closely applied to its fellow of the opposite side and within (dorsad of) the mylohyoid (Fig. 65, _c_).

_Origin_ from the ventral half of the inner surface of the mandibula for about one millimeter from the symphysis.

_Insertion_ by muscle-fibres into the lateral half of the ventral surface of the body of the hyoid bone.

_Relations._--Outer (ventral) surface with the stylohyoid (Fig. 65, _d_) and the mylohyoid (Fig. 65, _c_); medial border with the muscle of the opposite side. Lateral border with the hyoglossus (Fig. 67, _h_) and genioglossus (Fig. 67, _f_). Inner (dorsal) surface with the genioglossus.

_Action._--Draws the hyoid forward.

=M. jugulohyoideus= (Fig. 67, _b_).--The jugulohyoid is a small flat quadrangular muscle covering the outer part of the ventral surface of the tympanic bulla.

_Origin_ from the ventral border of the jugular process.

_Insertion_ into the caudal side of the cartilaginous part of the stylohyoid opposite the origin of the styloglossus.

_Relations._--Ventral surface with the digastric. Dorsal surface with the tympanic bulla (3).

_Action._--Draws the hyoid backward and thus gives a firmer surface of origin for the styloglossus.

=M. mylohyoideus= (Fig. 65, _c_).--The mylohyoid is a large thin muscle seen after the reflection of the digastric, filling with its fellow of the opposite side the whole angle between the rami of the lower jaw. Its fibres are transverse.

_Origin_ from the middle of the medial surface of the body of the mandible between the caudal opening of the mandibular canal and the symphysis of the jaw.

_a_, M. tragicus lateralis; _b_, M. jugulohyoideus; _c_, M.
pterygoideus externus; _d_, partially cut surface of M. pterygoideus
internus; _e_, M. styloglossus; _f_, M. genioglossus; _g_, M.
geniohyoideus; _h_, M. hyoglossus; _i_, M. glossopharyngeus; _j_, M.
constrictor pharyngis medius; _k_, M. constrictor pharyngis inferior;
_l_, M. stylopharyngeus; _m_, M. sternohyoideus (cut); _n_, M.
cricothyreoideus; _o_, M. sternothyreoideus (cut); _p_, M.
thyreohyoideus. 1, mandible; 1′, angular process of mandible; 2,
stylomandibular ligament; 3, bulla tympani; 4, trachea; 5, œsophagus;
6, thyroid gland; 7, isthmus of the thyroid gland.]

_Insertion_ with the opposite muscle into a median raphe which extends from the symphysis of the jaw to the hyoid bone and is closely united to the external surface of the geniohyoid. Some of the fibres gain insertion into the body of the hyoid bone through their insertion into the tendon of the stylohyoid (_d_).

_Relations_.--Outer surface with the submentalis (Fig. 64, _c_) and the digastric (Fig. 65, _b_). Lateral edge with the masseter (_a_), the digastric (_b_), and the mandibula. Caudal border with the stylohyoid (_d_). Inner (dorsal) surface with the geniohyoid (Fig. 67, _g_), the hyoglossus (Fig. 67, _h_), and the genioglossus (Fig. 67, _f_).

_Action_.--Raises the floor of the mouth and thus brings the hyoid forward.

=M. ceratohyoideus.=

_Origin_, the two proximal pieces of the cranial horn of the hyoid. The fibres pass caudad parallel to one another and within the middle constrictor of the pharynx.

_Insertion_ into the whole length of the caudal cornu of the hyoid bone.

_Relations_.--Outer surface with the middle constrictor of the pharynx. Inner surface with the pharynx.

_Action_.--Draws craniad the body of the hyoid by bringing its cornua together and bending the joint between the two pieces of the cranial cornua.

The muscles connecting the hyoid and the tongue are described in connection with the description of the tongue.