Chapter VIII: Section II: The Muscles (1)

THE MUSCLES.

LITERATURE.

Anonymous, Ueber das Schultergerüst der Schildkröten mit den
daran sitzenden Muskeln. Isis, 1827. (Contains remarks on the
shoulder-muscles of the frog.)

*Carus*, *C. G.* (1) Lehrbuch der vergleichenden Zootomie. 2nd Edit.
Leipzig, 1834. (2) Erläuterungstafeln zur vergleichenden Anatomie.
1 Part. 1826. (Muscles of the Leg.)

*Chappuis*, Morphologische Stellung der kleinen hintern Kopfmuskeln.
Zeit. f. Anat. u. Entwickl. 1876. Vol. II, pages 287–297.

*Cuvier*, Leçons d’anatomie comparée. Paris, 1835. Vols. I, II.

*Dugès*, Recherches anatomiques et physiologiques sur la déglutition
dans les Reptiles. Ext. des Annales des Sciences naturelles.
Paris, 1827.

*Dugès*, Leçons d’anatomie comparée. Paris, 1835.

*Duméril and Bibron*, Erpétologie générale ou Histoire complète des
Reptiles. 1836.

*Führbringer*, Zur vergleichenden Anatomie d. Schultermuskeln.
Jenaische Zeitschr. 1873. Vol. VII.

*Klein*, Beiträge zur Anatomie der ungeschwänzten Batrachier (Rana
temporaria, L.): in Jahrshefte des Vereins für vaterländische
Naturkunde in Würtemburg. 6 Jahrgang. 1850. Page 1.

*Kuhl*, Beiträge zur Zoologie der Rana esculenta: in Beitr. z. Zool.
Frankfurt, a. M. 1820. Page 115.

*de Mann*, Vergelykende myologische en neurologische studien over
Amphibien en Vogels. Acad. Proefschrift. 1873.

*de Mann*, Myologie comparée de l’extrémité post. chez les
amphibiens. Niederl. arch. f. Zool. 1874. Vol. II.

*Marshall*, The Frog. London and Manchester. 2nd Edit. 1885. Pages
60–71.

*Martin St. Ange*, Annales des sciences naturelles. Vol. XXIV. 1831.
Page 393.

*Meckel*, System der vergleichenden Anatomie. Halle, 1828. Vols. III
and IV.

*Pfeiffer*, Zur Anatomie des Schultergürtels und der Schultermuskeln
bei Säugethieren, Vögeln und Amphibien. Giessen, 1854.

*Rymer Jones*, Article ‘Reptiles’ in Todd’s Cyclop. of Anatomy and
Physiology. 1847–1852. Vol. IV. Page 263.

*Stannius*, Handbuch der Anatomie der Wirbelthiere. Vol. II. Zootomie
der Amphibien. Berlin, 1856.

*Wagner*, Icones Zootomicae. Leipzig, 1841.

*Wagner*, Lehrbuch der vergleichenden Anatomie. Leipzig, 1834–35.

*Zenker*, Batrachomyologia. Diss. Jena, 1825.

THE MUSCLES.

I. MUSCLES OF THE HEAD.

I. MUSCLES OF THE EYE.

*1.* _M. rectus inferior_ (Fig. 48 _ri′_).

*Dugès*, post-orbito-sous-oculaire, n. 12.--*Zenker*, _depressor
oculi_.

This muscle arises by a very thin, almost thread-like tendon from the parasphenoid, near the _foramen opticum_, and becomes rapidly broader; it lies beneath the tendon of the _membrana nictitans_ and a part of the _m. retractor bulbi_: then runs forwards and outwards to be attached into the lower part of the circumference of the eyeball.

Eye muscles of _Rana esculenta_, from below.

On the right side (_i. e._ in the left eye) the lev. bulbi (_l_) is taken away; on the left side it is still present.

_l_ M. levator bulbi.
_l.a_ M. lev. anguli scapulae
_oi_ M. obliquus inferior.
_os_ M. obliquus superior.
_p_ M. pterygoideus.
_r_ M. retractor bulbi.
_re_ M. rectus externus.
1 First cervical vertebra.
]

*2.* _M. rectus externus_ (Fig. 48 _re_).

*Dugès*, post-orbito-ex-oculaire, n. 14.

Arises by a thin, thread-like tendon from the parasphenoid near the _foramen opticum_, internal to and a little behind the _m. rectus inferior_: it then passes obliquely outwards over the _m. retractor bulbi_ and the tendon of the _membrana nictitans_, to be inserted into the outer and hinder part of the circumference of the eyeball.

*3.* _M. rectus internus_ (Fig. 48 _ri_).

*Dugès*, post-orbito-in-oculaire, n. 13.

A long, thin muscle, which arises by a thread-like tendon from the parasphenoid at the inner and hinder angle of the orbit, passes along its inner wall, and is inserted into the antero-internal part of the circumference of the eyeball.

*4.* _M. rectus superior_ (Fig. 49 _rs._).

*Dugès*, post-orbito-sous-oculaire.

Arises by a slender tendon from the fronto-parietal bone, widens rapidly, and runs forwards and outwards to be inserted into the upper part of the circumference of the _bulbus_.

Eye-muscles of _Rana esculenta_, from above.

_n_ Membrana nictitans.
_n′_ Tendon of membrana nictitans.
_p_ M. pterygoideus.
_rs._ M. rectus superior.
_t_ M. temporalis.
]

*5.* _M. obliquus inferior_ (Fig. 48 _oi_).

*Dugès*, pré-sous-orbito-oculaire.

This muscle arises near the floor of the orbital cavity, at the inner and anterior angle, from the palatine bone by a thin and long tendon, runs under Harder’s gland outwards and backwards, and is inserted, almost at a right angle with the axis of the eye, into the anterior part of the circumference of the eyeball.

*6.* _M. obliquus superior_ (Fig. 48 _os_).

*Dugès*, pré-sus-orbito-oculaire, n. 7.

The tendon of this small muscle arises from the inner end of the palatine bone, near the origin of the _m. obliquus inferior_, runs upwards, backwards, and outwards, and passes into a flat muscle, which rapidly becomes broader, and is inserted into the upper surface of the eyeball.

Eye-muscles of _Rana esculenta_, from below, the m. recti and obliqui have been removed.

_n′_ Tendon of membrana nictitans.
_r_ M. retractor bulbi, lower part.
_r′_ Second part of same.
]

*7.* _M. retractor bulbi_ (Figs. 48 _r_, 50 _r_, _r′_).

*Dugès*, orbito-post-oculaire or choanide, n. 10.--*Zenker*, _m.
opticus_.

This muscle surrounds the optic nerve, and is situated within the cone formed by the four recti muscles; it consists of three portions, which take their broad and fleshy (the _recti_ and _obliqui_ arise by thin tendons) origins from the under surface of the parasphenoid. The first portion (Fig. 50 _r_) arises from the under surface of the parasphenoid, nearly as far as the middle line, is broad and fleshy, and covers, from below, the tendon of the _rectus externus_, then runs forwards and outwards. The second portion (_r_′), which lies over this and the tendon of the _m. rectus externus_, has also a broad and fleshy origin, but runs more directly forwards, slightly crossing the preceding. The third portion arises above the two others by a strong thin tendon from the parasphenoid: it runs almost in the direction of the _m. rectus internus_, but more directly forwards. The first two portions pass more to the upper surface of the eyeball, the third more to the under surface; consequently the whole muscle forms a sheath surrounding the eyeball. The fibres to the upper surface of the eyeball are inserted somewhat in front of the equator of the eyeball, those to the under surface somewhat behind it.

*8.* _M. levator bulbi_, Dugès (Figs. 48 _l_, 51 _l_, 52 _l_).

*Dugès*, fronto-pterygoidien, n. 9.--*Klein*, _sustentator bulbi_.

Transverse section through the skull and orbital cavities of _Rana esculenta_.

_b_ Bulb of eye.
_c_ Skull cavity.
_g_ Mucous membrane.
_l_ M. levator bulbi.
_m_ Upper jaw.
_n_ Membrana nictitans.
_n_′ Continuation of same to the lower eyelid.
_p_ Upper eyelid.
]

_M. levator bulbi_ of _Rana esculenta_, seen from above; the eyeball which rests on it has been removed.

_d_._p_ M. depressor palpebrae inferioris.
_l_ M. levator bulbi.
_n_ Membrana nictitans.
_p_ M. pterygoideus.
_t_ M. temporalis.
]

There is no bony floor to the orbital cavity, and the oral and orbital cavities are only separated by soft tissues; these are:--the mucous membrane of the mouth, a thin fascia, and above this the muscle under consideration. The fibres of this muscle run from before and from the inner side obliquely backwards and outwards, below all the remaining muscles of the eye, with the exception of the origin of the _m. retractor bulbi_, and the tendons of the _m. obliquus inferior_, and the _m. pterygoideus_; they arise on the inner side from the upper and outer border of the fronto-parietal bone (Fig. 51), also from the transverse portion of the parasphenoid and pterygoid bones, anteriorly from the sphenethmoid and palatine bones; they run first downwards, then, in the direction indicated, underneath the eye; and are inserted externally by means of tendinous fibres into the superior border of the upper jaw.

*9.* From the foregoing muscle certain fibres pass to the lower
eyelid, which may be regarded as a *depressor palpebrae inferioris*
(Fig. 52 _d.p_).

Manz[42] has described a muscle as _depressor palpebrae inferioris_ which arises in the neighbourhood of the external angle of the eye, somewhat behind and below the lower border of the orbit, thence passes obliquely upwards to be inserted into the lower eyelid. This description is right as regards the insertion, but needs correction as regards the origin. The muscle is attached to the orbital border in so far that the tendinous expansion, into which the _levator bulbi_ passes at its external border, is attached into the upper jaw; this bundle splits off from the upper surface of the _levator bulbi_ at its middle, and runs outwards on the under surface of the eyeball to the hinder part of the lower eyelid.

[Footnote 42: Manz, Berichte der naturf. Gesellschaft zu Freiburg, 2 Band, 4 Heft, 1862, p. 391.]

Eye-muscles of _Rana esculenta_, from below, the m. recti and obliqui have been removed.

_n_′ Tendon of membrana nictitans.
_r_ M. retractor bulbi, lower part.
_r_′ Second part of same.
]

*10.* Tendon of the _membrana nictitans_[43] (Fig. 53 _n_′).

The pigmented free border of the nictitating membrane passes, at the inner and outer angles of the eye, into a tendon which passes for some distance through fibrous tissue, then descends to the under surface of the eyeball and joins that of the opposite side, so that the free border of the eyelid, together with this tendon, form a complete ring. The tendinous part of the ring, which is thin and thread-like, is found on the under surface of the eyeball, and lies under the _m. retractor bulbi_, and is bound to this muscle by connective tissue. Manz is right in saying that the two muscles described by Dugès as _levatores palpebrae inferiores_ (orbito-palpebral anterieur and posterieur, n. 5 and 6) do not exist; as is also the suggestion that he has confounded the tendon of the nictitating membrane with these; this is clearly shown in the figure in Plate VI of Dugès. With regard to the *actions* of these eye-muscles, it is plain that the four straight and two oblique muscles rotate the eyeball about three axes, one the axis of the eye, one vertical, and the third passing from behind forwards and inwards. The _m. retractor_ pulls the eyeball into the orbital cavity backwards and downwards, while the _levator_ raises it.

[Footnote 43: Compare Manz, _l. c._]

There is less agreement about the movements of the eyelids, or rather of the lower eyelid, for the upper has no independent movements. Dugès (_l. c._) says that the two muscles, which he considers to be _levatores palpebrae inferiores_, and which, according to him, are connected with the _m. retractor bulbi_, draw up the lid as it is being drawn backwards and downwards by the latter muscle. The depression of the lid on the relaxation of the retractor and projection of the eyeball is due simply to elasticity. Manz[44], on the contrary, has shown that the sinking of the eyeball by the contraction of the _retractor_ must necessarily cause a rising of the nictitating membrane, as its tendons are attached to that muscle and so must follow its movements.

[Footnote 44: _l. c._, p. 4.]

The depression of the lower lid occurs simultaneously with the raising of the eyeball by means of the _m. levator bulbi_, through the contraction of the _m. depressor palpebrae inferioris_, which proceeds from that muscle; this is easily understood, as they are but parts of the same muscle.

II. MUSCLES OF THE FACE.

*11.* _M. intermaxillaris s. dilatator narium_ (Fig. 54 _im_).

*Dugès*, intermaxillaire, n. 1.--*Zenker*, intermaxillaris medius.

This small muscle lies in the space between the vertical processes of the two premaxillary bones, and consists of obliquely-crossing fibres arising from the one bone and inserted into the opposite one. It brings together the processes of the intermaxillary bones, so that their upper extremities approach each other. At the same time, the cartilaginous nasal coverings or wings (_an_) diverge and the nares expand; hence we may regard this muscle as corresponding to a _dilatator narium_.

Facial muscles of _Rana esculenta_.

_an_ Cartilaginous nasal alae.
_i_′ Vertical process of premaxillary bone.
_im_ M. intermaxillaris.
_ln_ M. lateralis narium.
_n_ Cartilaginous nose capsule.
]

*12.* _M. lateralis narium_ (Ecker), (Fig. 54 _ln_).

*Zenker*, _m. intermaxillaris lateralis_.--*Klein*, _m. nasalis
inferior_.--*Dugès*, sus-maxillo-pré-nasal, n. 2.

This small muscle occupies the space between the anterior portion of the maxillary bone and the ascending process of the premaxillary bone. It arises from the maxillary, and ascends obliquely forwards to be inserted into the outer border of the ascending process of the premaxillary bone. It is antagonistic to the foregoing.

A third muscle is described by Dugès as _sus-maxillo-post-nasal_, n. 3 (_nasalis externus_, Klein); according to him it passes from the _proc. nasalis_ of the maxillary bone to the outer border of the nasal opening, which it widens. According to Klein (_l. c._, p. 9), this muscle in _R. temporaria_ runs to the upper border of the maxillary bone beneath the lower eyelid, and is long and narrow. I have, however, never been able to find muscular fibre in this situation.

III. MUSCLES OF THE LOWER JAW.

Muscles of the back and shoulder.

_c_ M. cucullaris.
_dm_,_dm_ M. depressor maxillae, arising from the fascia dorsalis.
On the right side it is cut through and reflected.
_fd_ Fascia dorsalis.
_fd_′ Same cut near the spinous processes.
_i_ M. infraspinatus.
_l.a_ M. levator anguli scapulae.
_ld_ M. latissimus dorsi.
_r_ M. retrahens scapulae.
_sc_ M. sternocleidomastoideus.
]

*13.* _M. depressor maxillae inferioris_, Carus, Zenker (Figs. 55,
56, 63 _d.m_.).

*Cuvier*, _l. c._, II, 141, _digastricus_.--*Dugès*,
sus-occipitodorso-angulaire, 32.

This is a strong, triangular muscle, wide above, pointed below. It is placed between the head and the shoulder-blade. It arises in two portions; the greater, from the _fascia dorsalis_ (_fd_), covers the scapula, and passes inwards and backwards over the muscles of the back; anteriorly it passes over the _m. temporalis_ and is attached to the fronto-parietal and squamosal, being continued to the fascia of the upper eyelid. The second part is smaller, and arises by fleshy fibres from the postero-superior arm of the squamosal, and from the posterior and inferior border of the cartilaginous tympanic ring. The two parts unite and are inserted into the hinder angle of the lower jaw. Cuvier correctly considers that only the anterior portion corresponds to the _digastricus_, the posterior answering to the _m. cervico-maxillaris_ of snakes. It draws the lower jaw down and opens the mouth.

*14.* _M. temporalis_ (Figs. 49, 52, 56, 57 _t_).

*Cuvier*, _m. temporalis_, I, _l. c._, p. 138.--*Dugès*,
sous-rupéo-temporo-coronoidien.

This muscle, together with the _M. pterygoideus_, occupies the space between the prootic and the eyeball; it arises by the greater part of its fibres from the upper surface of the prootic; it passes, narrowing, beneath the anterior arm of the squamosal, then over the pterygoid bone, between this and the maxillary and quadrato-jugal, receiving on the way other fibres which arise from the anterior border of the inferior arm of the squamosal and from the anterior circumference of the tympanic ring. The collected fibres end in a broad, flat tendon, which is inserted into the inner surface of the so-called _proc. coronoideus_.

Muscles of the lower jaw of _Rana esculenta_.

_d_ M. deltoideus.
_dm_ M. depressor maxillae, its origin where covering
the m. temporalis reflected at *.
_ld_ M. latissimus dorsi.
_m_ M. masseter.
_t_ M. temporalis, origin.
_t_′ Lower portion of same.
]

*15.* _M. pterygoideus_ (Figs. 49 _p_, 52, 57 _pt_).

*Cuvier*, _m. temporalis_, II, _l. c._--*Zenker*,
_m. massetericus_, _l. c._, p. 25.--*Dugès*,
pré-rupéo-pterygo-maxillaire, 31.

This is partly covered by the foregoing, and lies between it and the eyeball. It arises at the inner wall of the orbit from the fronto-parietal, and from that portion of the prootic which may be regarded as the _ala magna_, above the _m. retractor bulbi_. The muscle is broad, and compressed from before backwards: it runs downwards covered by the _m. temporalis_, and soon passes into a long, thin tendon (Fig. 57 _pt_), which is inserted, behind the _m. temporalis_ and immediately in front of the joint, into the inner surface of the lower jaw.

*16.* _M. masseter_ (Figs. 56, 57 _m_).

*Dugès*, zygomato-maxillaire, n. 29.

Arises as a somewhat broad muscle from the horizontal process of the quadrato-jugal and is inserted into the outer side of the lower jaw, opposite the insertion of the _m. temporalis_.

Muscles of the lower jaw of _Rana esculenta_.

_dm_ M. depressor maxillae cut through and reflected.
_la_ M. levator anguli scapulae.
_l.d._ M. latiss. dorsi, cut through and reflected.
_m_ M. masseter.
_pt_ M. pterygoideus.
_s_ Scapula.
_s_′ Suprascapula.
_s.c._ M. sternocleidomastoideus.
_t t_ M. temporalis cut through and reflected.
]

*17.* _M. submaxillaris_ (Figs. 58, 59, 61 _sm_, _sm_′).

*Cuvier*, _m. mylo-hyoideus_, _l.c._, II, 536.--*Zenker*,
_mylo-sternoideus_, p. 25.--*Dugès*, sous-maxillaire, n. 15.

This muscle forms the floor of the mouth as does the _mylo-hyoideus_ in man; it is, however, not inserted into the hyoid bone.

It arises--1. From the whole of the inner surface of the upper border of the lower jaw[45], except near the angle (Fig. 58 _sm_);

[Footnote 45: A second origin from the lower border of the mandible, described by Klein, is not to be found. The appearance is due to the exit of vessels and nerves from the groove between the mandible and the muscle.]

2. By a small portion (Figs. 58, 59, 61 _sm_′) near the skull, from the cartilaginous anterior cornu of the hyoid-bone which projects from the cartilaginous part of the prootic bone. This portion descends along the cornu to unite with the other portion. The two together form a membranous layer, the fibres of which run transversely and meet in a band of connective tissue along the middle line, forming a kind of _linea alba_. The sheath runs forwards to the most projecting part of the lower jaw superficially to the _m. submentalis_. Slightly in front of its posterior border the muscle is attached in its whole breadth to the skin of the throat by a fine lamella of connective tissue, which is not always complete. The posterior border of the muscle is attached to a fascia, which passes between the deeper muscles and is attached to these. It is known that this muscle plays an important part in the movements of respiration and swallowing; but its precise action has not yet been worked out.

*18.* _M. submentalis_ (Fig. 59 _smt_).

*Cuvier*, _transversus_, _l. c._, p. 588.--*Dugès*, 4,
sous-mentonnier.--*Zenker*, _m. lingualis_ (incorrectly brought
into connection with _m. hyoglossus_).

This small muscle lies in the anterior angle of the lower jaw between the dentary bones. It consists of transverse fibres which pass from one bone to the other. Below it is covered by the most anterior portion of the _m. submaxillaris_.

Muscles of the throat, chest, and abdomen of _Rana esculenta_.

_sm_ M. submaxillaris.
_sm_′ Hinder portion of same arising from
the anterior cornu of the hyoid bone.

(For other references see page 68.) ]

Its action is to approximate the sides of the lower jaw: according to Dugès (_l. c._, p. 123), it assists in closing the nostrils, by drawing together the sides of the lower jaw and thus raising the premaxillae.

IV. MUSCLES OF THE HYOID BONE AND THE TONGUE.

*19.* _M. geniohyoideus_ (Figs. 59 _gh_, 60 _gh_).

*Cuvier*, IV, 1, 536.--*Dugès*, n. 16.--*Zenker*, p. 30.--*M. St.
Ange*, _l. c._, Pl. XXVI, f. 1, 13, p. 423.

Arises from the lower jaw in two portions, the one from near the middle line above the _m. submentalis_, the other more externally from the upper border of the lower jaw. The two parts unite to form a long, flat muscle, which lies on the ventral surface of the body of the hyoid bone, and divides posteriorly into two portions. One of these, the median (Figs. 59, 60 _gh_″), is inserted into the inner border of the posterior horn of the hyoid bone, and is here attached to a fascia which covers the _m. hyoglossus_ from beneath. By the same fascia the muscles of opposite sides are connected in the space between the two posterior cornua. The lateral division (Figs. 59, 60 _gh_′) is attached to the posterior cartilaginous process of the hyoid bone.

Muscles of the hyoid bone and the tongue of _Rana esculenta_.

The m. submaxillaris has been removed close to its insertion.

_cm_′ Origin of the hinder portion of same from the hyoid bone.
_gh_ M. geniohyoideus.
_gh_′ External portion of same.
_gh_″ Internal portion of same.
_H_ Body of hyoid bone.
_H_′ Anterior horn.
_hg_ M. hyoglossus.
_oh_ M. omohyoideus.
_ph_ Mm. petrohyoidei.
_sh_ M. sternohyoideus.
_sh_′ External origin of same.
_sh_″ Internal origin of same.
_sm_ M. submaxillaris.
_sm_′ Origin of hinder portion of same.
_smt_ M. submentalis.
]

*20.* _M. sternohyoideus_ (Figs. 59 60 _sh_).

*Cuvier*, IV, 1, 538 (_pubio-hyoideus_).--*Dugès*, n. 17,
sterno-xipho-hyoidien.--*Zenker*, p. 30.

This muscle forms the cervical part of the _m. rectus abdominis_ and is, in fact, a direct continuation of it. It arises by an inner portion (Fig. 59 _sh_″) from the upper surface of the inner extremity of the coracoid and from the xiphisternum, while the outer portion (_sh_′) is an immediate continuation of the _m. rectus abdominis_, which passes into this muscle at about the fifth _inscriptio tendinea_. The muscle passes forwards on the upper surface of the coracoid and of the clavicle, under the pericardium towards the hyoid bone; here the muscle, hitherto horizontal, suddenly becomes (compare Fig. 60) vertical, and passes between the two insertions of the _m. geniohyoideus_, and is inserted for a considerable length into the lower surface of the hyoid bone and the anterior extremity of the posterior cornu.

Muscles of the tongue and of the hyoid bone of _Rana esculenta_, from below.

_gh_ M. geniohyoideus.
_gh_′ External origin }
_gh_″ Internal origin } of same.
_H_ Body of hyoid.
_H_′ Anterior cornu.
_H_″ Posterior cornu.
_hg_ M. hyoglossus.
_hg_′ Hinder origin of same.
_oh_ M. omohyoideus.
_ph_. 1, 2, 3, 4, first, second, third, and fourth
m. petrohyoideus.
_sh_ M. sternohyoideus.
]

*21.* _M. omohyoideus_ (Figs. 59, 60 _oh_).

*Cuvier*, _l.c._, p. 539.--*Dugès*, n. 18, interscapulo-hyoidien ou
omohyoidien.-- *Zenker*, p. 31.--*M. St. Ange*, _l.c._

Arises from the anterior border of the bony scapula, and is inserted into the outer part of the ventral surface of the body of the hyoid: it is partially covered by the _m. sternohyoideus_.

*22.* _M. petrohyoideus anterior_ (Ecker), (Fig. 61 _ph_1).

*Dugès*, 10, rupéo-cérato-hyoidien.--*Zenker*, _m. petro-ceraus_?
p. 30.-- *Klein*, _basio-hyoideus_, _l.c._, p. 71.

A thin, flat muscle, narrow above, but broadening rapidly below, which arising from the outer extremity of the prootic bone, partially surrounds the pharynx below, into which some of its fibres are inserted; it is attached to the ventral surface of the body of the hyoid bone, near the lateral notch. The chief action of this muscle appears to be that of a _m. constrictor pharyngis_.

*23, 24, 25.* _Mm. petrohyoidei posteriores_ (Ecker), (Figs. 61
_ph_ 2, 3, 4).

*Cuvier*, _mm. stylohyoidei_, _l. c._, p. 537.--*Dugès*, 20, 21,
22, masto-hyoideus (Fig. 4).--*Zenker*, _petro-hyoideus superior_
and _inferior_.--*Klein*, _stylo-hyoideus_, _l. c._, p. 18.

These are three long, thin muscles, which lie nearly parallel to one another, and run from the prootic bone to the posterior cornu of the hyoid bone. All three arise, covered by the _m. sternocleidomastoideus_, from the lateral extremity of the prootic, pass round the pharynx and are attached, the _m. petrohyoideus posterior primus_ (Fig. 61 _ph_ 2) to the anterior extremity, the _secundus_ (Fig. 61 _ph_ 3) to the middle; and the _tertius_ (Fig. 61 _ph_ 4) to the hinder extremity of the posterior horn of the hyoid bone.

*26.* _M. hyoglossus_ (Figs. 59, 60, 61 _hg_).

*Cuvier*, _l. c._, p. 588.--*Dugès*, 24, hyo-glosse.

Arises from the bony posterior extremity of the hinder process of the hyoid bone (_hg_′). The muscles of the two sides pass forwards and converge to the middle line, where they unite. The azygos muscle thus formed runs forwards on the ventral surface of the hyoid bone, between the _mm. geniohyoidei_, over the anterior border of the hyoid, and passes into the tongue, where it turns backwards and runs to the tip. (For action, see tongue.)

Muscles of the hyoid bone of _Rana esculenta_, seen from the right side and below.

_H_′ Anterior cornu.
_H_″ Posterior cornu.
_hg_ M. hyoglossus.
_H H_ Body of hyoid bone.
_ph_ 1 M. petrohyoideus anterior.
_ph_ 2, 3, 4 Mm. petrohyoidei posteriores.
_sm_ M. submaxillaris.
_sm_′ Hinder portion of same.
]

*27.* _M. genioglossus._

*Cuvier*, _l. c._, p. 587.--*Meckel*, _l. c._, IV, 339.--*Dugès*,
23, genio-glosse.

Arises above the insertion of the _m. geniohyoideus_ on either side near the middle line from the two anterior bones of the lower jaw. The two origins quickly unite to form a thick, very firm muscular belly, which in its course backwards rapidly thins, and is distributed by numerous bundles; decussating with the fibres of the _m. hyoglossus_ at an acute angle, it runs on to the anterior extremity of the tongue.

II. MUSCLES OF THE TRUNK.

I. MUSCLES OF THE ABDOMEN.

In the formation of the abdominal wall the following muscles take part:--(1) _m. rectus abdominis_, (2) _m. obliquus externus_, (3) _m. obliquus internus_, (4) the _portia abdominalis_ of the _m. pectoralis_. Above, the _m. obliquus internus_ forms a kind of *diaphragm*, partially separating the abdominal from the thoracic cavity (p. 70).

*28.* _M. rectus abdominis_ (Fig. 62 _r_).

*Dugès*, pubio-thoracique, n. 52.

These muscles, situated on either side of the middle line of the abdomen, are as a rule traversed by five notched _inscriptiones tendineae_. Each muscle arises, by a narrow, strong tendon, from the inferior border of the pubes, passes forwards, and quickly widening, divides at the second _inscriptio tendinea_ (counting from behind) into two portions.

(_a_) The Outer portion (Fig. 62 _r_) runs into the _portio abdominalis_ of the _m. pectoralis_, and forms the greater lateral division of that muscle.

(_b_) The Inner (_r_′) continues as the _m. rectus abdominis_ and gradually narrows anteriorly. At the sternum some of the fibres (the median) are inserted into the dorsal surface of the cartilaginous plate of the xiphisternum, while the greater part of the muscle continues forwards over the coracoid to become the _m. sternohyoideus_ at about the fifth _inscriptio tendinea_ (p. 64).

*29.* _M. obliquus externus_ (Fig. 63 _oe_, _oe_′).

*Zenker*, _l. c._, p. 31, _m. obliquus_.--*Dugès*,
dorso-sous-abdominal, n. 54.

The _m. obliquus externus_ arises from--

(_a_) The aponeurosis covering the long muscles of the back, and by this from the spinous processes. The anterior edge of the _m. obliquus externus_ covers the posterior edge of the _m. latissimus dorsi_, which arises from the inferior, ventral surface of the aponeurosis. The aponeurosis also divides laterally into two parts, one of which, the posterior, passes into the _obliquus externus_, while the anterior forms the tendon of origin of the _depressor maxillae inf._ (_dm_) (compare Fig. 66).

(_b_) A second, narrow portion, _portio omo-abdominalis_ (Fig. 63 _oe_′) (_m. xipho-adscapulaire_, Dugès, n. 62), arises from the posterior border of the scapula by a thin tendon, and becomes broader as it runs downwards and backwards, to join the anterior border of the other and larger portion.

Muscles of the chest, throat, and belly of _Rana esculenta_.

_ch_ M. coraco-humeralis.
_d_ M. deltoideus.
_oi_ M. obliquus abdom. internus.
_oe_ M. obliq. abdom. externus.
_oe_′ Scapular portion of same.
_oh_ M. omohyoideus.
_p_′ Port. sternalis anterior of m. pectoralis.
_p_″ Port. sternalis posterior of same.
_p_‴ Port. abdominalis of same.
_r_ M. rectus abdominis.
_r_′ Inner portion of same.
_sh_ M. sternohyoideus.
_sm_ M. submaxillaris.
_sm_′ Hyoid origin of same.
_sr_ M. sternoradialis.
]

The whole muscle is attached by its most anterior fibres to the cartilage of the xiphisternum, the rest passing into an aponeurosis which, inseparably connected with the _inscriptiones tendineae_, traverses the lower surface of the _m. rectus abdominalis_ to the _linea alba_.

Muscles of trunk of _Rana esculenta_, from the right side.

_cd_ M. cutaneus femoris.
_d_ M. deltoideus.
_d.m._ M. depressor maxillae.
_i_ M. infraspinatus.
_ld_ M. latiss. dorsi.
_oe_ M. obliquus abdom. externus.
_oe_′ Scapular origin of same.
_ss_ M. subscapularis.
_t_ M. triceps brachii.
]

*30.* _M. obliquus internus_ (and _transversus_), (Figs. 64, 65
_oi_).

*Dugès*, ileo-transverso-sous-sternal, p. 53.--*Zenker*,
_transversus_, _l. c._, p. 31.--*Kuhl*, _transversus_, _l. c._,
p. 116.

This muscle corresponds with the combined _obliquus internus_ and _transversus_, and has therefore been described either as the one or the other, by various authors.

The fibres arise tendinously--

*a.* From the transverse processes of the vertebrae from the fourth backwards, and from the fascia covering the _mm. intertransversarii_.

*b.* From the iliac bone, by a strong tendon from its upper border, and by a few weaker fibres from its outer surface. The latter fibres are covered by the former, and these end posteriorly in a sharp concave border.

The muscular bundles diverge from these points, some running forwards, some backwards; the former are only partially covered by the _portio omo-abdominalis_ of the _m. obliquus externus_ (compare Figs. 62, 63), in front of the anterior edge of that muscle. The posterior border of the muscle is uncovered.

Second layer of abdominal muscles of _Rana esculenta_, from the right side and below. The m. obliquus externus and the right anterior extremity has been removed.

_dm_ M. depressor maxillae.
_hg_ M. hyoglossus.
_ld_ M. latissimus dorsi and infraspinatus.
_oi_ M. obliquus internus.
_oi_′ Insertion of third portion of same.
_oi_″ Second portion inserted into the pharynx.
_pc_ Pericardium.
_ph^4._ M. petrohyoideus quartus.
_r_ M. rectus abdominis.
_ss_ M. subscapularis.
]

The insertions of the muscle are very various, and as a consequence very various functions are accomplished by it.

*a.* The most anterior part of the muscle (Fig. 65 _oi_‴), the fibres of which run forwards, is attached--

1. Partly to the xiphisternum and the coracoid.

2. A second portion, _viz._ that arising from the transverse processes of the fourth vertebra (Fig. 64 _oi_″), surrounds the pharynx like a diaphragm (Fig. 65 _oe_), and is attached to its side as far as the dorsal aspect (Fig. 65 _oi_′). This portion is lightly separated from the following.

3. A third portion, placed behind the preceding, runs from the pharynx over the pericardium (Fig. 64 _pc_), and is attached to this nearly as far as the middle line (Figs. 64 _oi_′ and 65 _oi_″), resting on the sternum, the _m. rectus_ and _m. sterno-hyoideus_. The lines of insertion of the muscles of opposite sides form an angle, open in front. In the thin borders of this portion the muscular bundles lie almost entirely in simple layers, and they are therefore well adapted for microscopical purposes.

*b.* The middle and posterior portions of the muscle pass downwards and slightly backwards, towards the outer border of the _m. rectus_; there they pass into a tendon which, for the most part, runs on the upper surface of the _rectus_ to the _linea alba_.

II. MUSCLES OF THE BACK.

The muscles of the back are covered by a fascia, the *fascia dorsalis* (Fig. 66 _fd_), attached to the spinous processes of the vertebrae. Anteriorly, where it covers the _m. temporalis_, it is attached to the fronto-parietal and squamosal bones, posteriorly to the superior border of the iliac bones and the extremity of the urostyle. The posterior part, which covers the origins of the _m. longissimus dorsi_, of the _m. coccygeo-iliacus_, and of the _coccygeo-lumbaris_, is especially strong. From the anterior part several muscles arise laterally, viz. a portion of the _m. obliquus abdominalis externus_, of the _m. latissimus dorsi_, and of the _m. depressor maxillae inferioris_. In the uppermost layer, immediately covered by the _fascia dorsalis_, lie the _m. cucullaris_, the _m. retrahens scapulae_, the _m. latissimus dorsi_ arising from the fascia itself, and the scapula with its muscles; then come the long muscles of the back; and in the third and deepest layer the short muscles of the back.

M. obliquus internus, showing its attachments superiorly.

_h_ Xiphisternum.
_oe_ Oesophagus.
_oi_ M. obliquus internus.
_oi_′ Fibres of m. obliq. int., which are inserted
into the oesophagus.
_oi_″ _oi_‴ Fibres of same, which are attached to
coracoid and xiphisternum.
_p_ Pericardium.
_r_ M. rectus abdominis.
]

The individual muscles are as follows:--

A. _LIMB MUSCLES OF THE BACK_ (for moving the shoulder-girdle and arm).

*31.* _M. cucullaris_ (Fig. 66 _c_).

*Cuvier*, _angularis_.--*Dugès*, n. 38, sous-occipito
adscapulaire.--*Zenker*, _levator scapulae sublimis_.

In order to see this muscle, it is necessary to separate the _fascia dorsalis_ from the spines of the vertebrae and to turn it back with the _m. depressor maxillae inf._ arising from it. It is then seen to rise from the posterior surface of the exoccipital as far as the middle line; the muscles of the two sides run backwards, diverging each from the other, so as to form an angle, and are then attached on each side to the anterior superior angle of the suprascapula at its under surface and median border.

Cuvier considers this muscle as the analogue of the _m. levator anguli scapulae_. Dugès and Meckel consider it to be the anterior part of the _m. cucullaris_, the former thinking the posterior part of the muscle to be the _m. rhomboideus_. I cannot agree with these opinions, and I regard the muscle as simply representing the _m. cucullaris_ of man (Ecker).

*32.* _M. latissimus dorsi_ (Figs. 56, 66 _ld_).

*Dugès*, n. 66, lombo-huméral.--*Zenker*, _depressor brachii_.

This thin, triangular muscle arises from the ventral surface of the _fascia dorsalis_, and is posteriorly covered in part by the anterior border of the _m. obliquus abdominis externus_. The muscle becomes narrower towards the sides, and passes into a flat tendon, which blends with that of the _m. infraspinatus_, and is attached to the outer surface of the _crista deltoidea_ of the humerus by a triangular expansion.

*33.* _M. retrahens scapulae_ (Ecker), (Fig. 66 _r_).

*Dugès*, n. 59, lombo-adscapulaire.--*Klein*, _m. rhomboideus_, _l.
c._, p. 26.--*Zenker*, _omoplateus rectus_? p. 37, _l. c._--*Kuhl*,
_l. c._, 124, _retrahens rhomboideus_.

Muscles of the back and shoulder-blade.

_c_ M. cucullaris.
_dm_ M. depressor maxillae arising from the fascia dorsalis,
cut through and reflected on the right side.
_fd_ Fascia dorsalis.
_fd_′ Same cut through at the spines.
_i_ M. infraspinatus.
_l.a_ M. levator anguli scapulae.
_ld_ M. Latissimus dorsi.
_r_ M. retrahens scapulae.
_sc_ M. sternocleidomastoideus.
]

This flat, oblong muscle arises from the transverse process of the fourth vertebra, and is connected with the third tendinous inscription (counting from before) of the _m. longiss. dorsi_. Posteriorly its origin forms a convex border, whence it runs forwards and to the side; it is inserted into the ventral surface of the suprascapula, near its inner border. This muscle lies near the _m. serratus_ or _transv. scap. tertius_ (Fig. 68 _ts_″), and has an analogous position. It would, therefore, possibly be more correct to regard it also as a _m. serratus_. It arises from parts which represent ribs, and is inserted into the scapula. It has, at any rate, no analogy to the _m. cucullaris_, with which Dugès connects it, nor with the _m. rhomboideus_, which Klein holds it to be, as it does not arise from spinous processes.

B. _LONG MUSCLES OF THE BACK._

*34.* _M. extensor dorsi communis_ (Fig. 67 _lg.d._).

*Dugès*, n. 33–40, masse des muscles surspinaux devisée en
huit faisceaux principaux: 1. vertebro-sus-occipital, 2–5.
transverso-spinaux, 6. transverso-coccyg., 7. sacro-coccygien,
8. ileo-coccygien. The muscles 1–7 form the lombo-costal, 8 the
ischicoccyg., Cuv.--*Zenker*, _m. sacrolumbaris_.--*Klein*,
_longiss. dorsi_, _coccygeo-lumb._, _coccyg.-iliac_.

This muscular mass is covered by the _fascia dorsalis_, the _m. cucullaris_ and _retrahens scapula_, and the suprascapula: it corresponds with (1) the _m. ileo-costalis_ and _longissimus dorsi_, _dorsi_ and _cervicis_ (Henle); (2) the _semispinalis_ and _spinalis_ (Henle).

The following separate portions may be made out:--

*35.* (1) _M. longiss. dorsi_ (Fig. 67 _lg.d._).

This muscle arises from the most anterior part of the urostyle, runs forwards near the middle line, separated from the muscle of the opposite side by the spinous processes of the vertebrae. The inner portion passes over the posterior spinous processes without being connected with them, as far as the fifth, it is then inserted into the succeeding spines as far as the exoccipital bone. The lateral portion runs outwards and forwards to be attached to the transverse processes and oblique processes of all the vertebrae, from the sixth forwards, while accessory muscular slips arise from the transverse processes and from the anterior spinous processes which, merging in the general muscle-mass, are inserted with this into the occiput.

The muscle is subdivided by a series of wavy, tendinous partitions (Fig. 67), which arise from the transverse processes, and traverse the muscle in planes, the upper surfaces of which are directed upwards and forwards. This arrangement of the muscle indicates its relation with the lateral trunk muscles of fish and fish-like amphibians.

*36.* (2) _M. coccygeo-sacralis_ (Fig. 67 _c.l._).

This muscle is partially covered by the preceding, it arises from the lateral surfaces of the anterior half of the urostyle; from this origin the fibres pass forwards and outwards to be inserted in two portions, the anterior set into the arch and the posterior set into the transverse process of the last vertebra. The former may be regarded as _m. intercruralis_, the latter as _m. intertransversarius_.

*37.* (3) _M. coccygeo-iliacus_ (Fig. 67 _c.i._).

This muscle arises from nearly the whole length of the lateral surface of the urostyle, the anterior portion being concealed by the preceding muscle. The fibres pass outwards and forwards to be inserted into the anterior two-thirds of the inner surface of the ilium.

Muscles of the back and pelvic girdle of _Rana esculenta_.

_c.i._ M. coccygeo-iliacus.
_c.l._ M. coccygeo-sacralis.
_g.l._ M. glutaeus.
_i_ MM. intertransversarii.
_i′_ MM. intercrurales.
_i.c.i._ M. intertransv. capitis inferior.
_i.c.s._ M. intertr. cap. sup.
_il._ M. ilio-lumbaris.
_lg.d._ M. longissimus dorsi.
_o.i._ M. obliq. internus.
_t_ M. temporalis.
]

*38.* _M. ilio-lumbaris_ (Klein), (Fig. 67 _il._).

*Dugès, n.* 51, transverso-iliaque.--*Cuvier*, *Zenker*, etc.,
_quadr. lumborum_.

Evidently represents the _quadratus lumborum_ of human anatomy; it takes its origin from the anterior extremity of the ilium, and runs forwards to be inserted into the transverse processes of the vertebrae from the seventh to the fourth.

C. _SHORT MUSCLES OF THE BACK._

*39.* _M. intertransversarius capitis superior_ (Ecker), (Fig. 67
_i.c.s._).

*Dugès*, n. 41, ex-occipito-transversaire sup.

A small muscle arising from the prootic: it lies above the _levator anguli scapulae_, and is inserted into the transverse process of the second vertebra.

*40.* _M. intertransversarius capitis inferior_ (Fig. 67 _i.c.i._).

*Dugès*, n. 42, ex-occipito-transv. inf.

This muscle lies on the ventral surface of the preceding one, but is easily separable from it; it arises from the angle of the prootic and is inserted, together with the preceding muscle, into the transverse process of the third vertebra. The _n. vagus_ passes outwards between these two muscles.

*41.* _MM. intertransversarii dorsi_ (Fig. 67 _i_).

*Dugès*, n. 43 to 50, intertransversaires.

Seven small muscles, placed between adjacent transverse processes of the vertebrae; from the second to the last, in continuity with the muscles last mentioned.

*42.* _MM. intercrurales_ (Ecker), (Fig. 67 _i_′).

*Klein*, p. 29, interspinales, interobliqui.

Those muscular fibres found between the arches of adjacent vertebrae are so named. On account of the shortness of the spinous processes they can scarcely be named _m. interspinales_.

III. MUSCLES OF THE ANTERIOR EXTREMITY.

I. MUSCLES OF THE SHOULDER-GIRDLE.

A. _DORSAL MUSCLES OF THE SHOULDER-BLADE_.

(I.) Muscles arising from the head or trunk, and inserted into the scapulae, which they act upon primarily, and upon the shoulder-girdles secondarily.

Some of these muscles, such as _m. cucullaris_ and _retrahens_, are situated on the back, and have already been described with the muscles of that region. Others are attached partly to the under-surfaces of the scapulae and are only visible from below; they are best seen in such a preparation as is shown in Fig. 68, made by cutting through the sternum in the middle line, and reflecting each half outwards.

(*a*) _Muscles which arise from the skull_.

*43.* _M. levator anguli scapulae_ (Fig. 68 _la_).

*Dugès*, sous-occipito-adscapulaire, n. 60.--*Zenker*, _protractor
scapulae_, Pl. I, Fig. 5.--*Cuvier*, Leçons I, p. 379, describes
this muscle as part of the _m. serratus anticus magnus_.

A fairly strong muscle, which has a broad origin from the prootic and exoccipital bones as far as the _foramen magnum_, a few fibres are also attached to the lateral portions of the parasphenoid. The fibres run backwards and outwards, first in a frontal plane and then in a sagittal plane, to be inserted into the under surface of the suprascapula near the posterior border, where it encloses the hinder border of the _m. interscapularis_.

Its action is to draw the shoulders forwards and inwards, or the head downwards.

*44.* _M. sternocleidomastoideus_ (Fig. 68 _sc_).

*Dugès*, scapulo-mastoidien, n. 65.--*Cuvier*,
sterno-mastoidien.--*Zenker*, _protractor scapulae_, Pl. I, Fig. 5,
1.

A narrow muscle placed in front of and externally to the preceding muscle; its general direction resembles that of the _m. levator ang. scap_.

The fibres arise from the most external part of the prootic and from the hindermost part of the squamosal, under cover of the _m. digastricus maxillae_, and from the hinder portion of the cartilaginous tympanic ring. Covered by these muscles, it passes backwards and downwards to be inserted into the concavity of the anterior border of the scapula; externally to the origin of the deltoid.

The action of this muscle is to draw the shoulder forwards and towards the middle line, or to bend the head downwards.

*45.* _M. protrahens scapulae_ (Fig. 68 _ps_).

*Dugès*, *Zenker*, _protractor acromii_, Pl. I, Fig. 5, 3.

This muscle lies to the outer side of the _rectus capitis inferior_: it arises from the prootic, and runs backwards and outwards upon the _levator anguli scapulae_, to be inserted into the scapula.

It pulls the scapula forwards.

(*b*) _Muscles which arise from the vertebrae._

*46.* _M. transverso-scapularis major_ (Ecker), (Fig. 68 _ts_).

*Dugès*, transverso-interscapulaire, n. 63.--*Cuvier*,
_l. c._, p. 380, probably regarded as a portion of the
_serratus_.--*Zenker*, Pl. I, Fig. 5, 3; _depressor acromii_,
Pl. II, Fig. 3, 15.--*Klein*, _depressor scapulae_.

This muscle arises by tendon from the cartilage of the transverse process of the fourth vertebra and by a slip from the cartilage of the transverse process of the third vertebra. Diminishing in size, the muscle passes outwards, forwards, and upwards to be inserted into the posterior border of the scapula, opposite the insertion of the _m. sternocleidomastoideus_. It draws the shoulder inwards, backwards, and downwards.

*47.* _M. transverso-scapularis minor_ (Ecker), (Fig. 68 _ts_′).

*Dugès*, transverso-adscapulaire, n. 61.--*Cuvier*, regarded as
part of the _serratus_.--*Zenker*, Pl. I, Fig. 5, 7, _detractor
scapulae_.

This is much shorter than the muscle just described; it arises under cover of the _m. levator scapulae_, from the transverse process of the third vertebra in front of the _transverso-scapularis major_; and runs outwards and forwards to be inserted into the ventral surface of the cartilage of the scapula. The action of the muscle is to draw the shoulder inwards, backwards, and outwards. Dugès regards this muscle as a portion of the _serratus anticus magnus_, the remainder of which he considers is to be found in the _portio scapularis_ of the _m. obliquus externus_ (xipho-adscapulaire, Dugès, n. 62).

Muscles of the shoulder, from below; the sternum has been cut through and the sides drawn apart.

_d_ Deltoideus.
_is_ Interscapularis.
_it_ Intertransversarii.
_la_ Lev. anguli scapulae.
_ps_ Protrahens scapulae.
_sc_ Sternocleidomastoideus.
_ss_ Subscapularis.
_ts_ Transverso-scap. major.
_ts_′ Transverso-scap. minor.
_ts_″ Transverso-scap. tertius.
]

*48.* _M. transverso-scapularis tertius s. serratus_ (Ecker),
(Fig. 68 _ts_″).

This is larger than the muscle just described; arising by a broad and flat origin from the transverse processes of third and fourth vertebrae, it runs upwards and inwards to be inserted into the ventral surface of the cartilaginous scapula near its inner border. In position, course, and action the muscle most nearly represents the _m. serratus anticus_ of human anatomy.

(II.) Muscles on the scapula, that is, arising from the scapula and inserted into the scapula or humerus.

(*a*) _Muscles on the deeper surface._

*49.* _M. interscapularis_ (Fig. 69 _i.s._).

*Dugès*, interscapulaire, n. 64.

Muscles of right shoulder and upper arm. The coracoids (_co_) and the clavicles (_cl_) have been drawn apart after cutting through the sternum.

_c.h._ M. coraco-humeralis.
_cl_ Clavicle.
_c.o._ Coracoid.
_d_ M. deltoideus.
_d_′ Clavicular portion of m. deltoideus.
_i_ M. infraspinatus.
_i.s._ M. interscapularis.
_l.a._ M. levator anguli scapulae.
_l.d._ M. latissimus dorsi.
_p_′ Sternal portion of m. deltoideus.
_p_″ Anterior sternal portion of the m. pectoralis.
_p_‴ Posterior sternal portion of the m. pectoralis.
_s_ Scapula.
_s.r._ M. sternoradialis.
_t.r._ M. triceps brachii.
]

One end of this muscle is tendinous, and is attached to the outer extremity of the suprascapula; from this the muscle, becoming fleshy and narrower, runs towards the middle line to become attached to the ridge on the ventral surface of the scapula, from which the _m. deltoideus_ and the _m. subscapularis_ arise, and between which it passes. It approximates the scapula and suprascapula and lessens the angle between them.

*50.* _M. subscapularis_ (Fig. 70 _ss_).

*Dugès*, sous-scapulo huméral, n. 72.

This muscle is situated on the upper or visceral surface of the scapula. It arises from a bony ridge found on the upper surface of the coracoid and of the _proc. coracoideus_ of the scapula. The muscle runs outwards and is inserted, after widening, into the inner surface of the _crista deltoidea_ of the humerus; it is antagonistic to the deltoid, and draws the raised arm backwards and towards the trunk.

Right shoulder, from below, arm strongly abducted.

_cl_ Clavicle.
_co_ Coracoid.
_d_ Deltoideus.
_d_′ Clavicular portion of deltoid.
_h_ Humerus.
_ss_ Subscapular muscle.
]

(*b*) _Muscles on the superficial surface._

*51.* _M. infraspinatus_ (Fig. 57, between _ld_ and _dm_, Fig. 71
_i_).

*Dugès*, adscapulo-huméral, n. 67.

The _m. infraspinatus_ represents the _m. infraspinatus_, _teres major_ and _minor_ of human anatomy. It is of triangular form, with the broad base directed inwards; it arises from the whole of the upper surface of the suprascapula except along the inner border which is formed of hyaline cartilage alone: from this origin the fibres converge outwards to a flat tendon which unites with that of the _m. latissimus dorsi_ to be inserted into the _crista deltoidea humeri_, by means of a thin, triangular, tendinous expansion.

Muscles of the back and shoulder.

_c_ M. cucullaris.
_dm_ M. depressor maxillae.
_fd_ Fascia dorsalis.
_fd_′ Fascia dorsalis reflected.
_i_ M. infraspinatus.
_l.a_ M. levator anguli scapulae.
_ld_ M. latissimus dorsi.
_r_ M. retrahens scapulae.
_sc_ M. sternocleidomastoideus.
]

*General arrangement of the muscles of the shoulder-blade.*

The muscles attached to the scapula and suprascapula are:

1. Muscles of the back (_m. cucullaris_ and _m. retrahens scap._).

2. Muscles of the neck (_m. omohyoideus_).

3. Muscles of the abdomen (_portio scapularis_ of the _m. obliquus externus_).

4. True shoulder muscles (_m. levator anguli scapulae_; _m. sternocleidomastoideus_; _m. protrahens scapulae_; _mm. transverso-scapularis major_, _minor_, and _tertius s. serratus_; _m. interscapularis_; _m. subscapularis_; and the long head of the _m. triceps_).

*From above* the following are visible: _m. cucullaris_, a portion of the _m. subscapularis_, and the _transverso-scapularis maior_.

*From below* (after cutting through and drawing aside the two halves of the sternum) may be seen: the _omohyoideus_, _sternocleidomastoideus_, _levator anguli scapulae_, _protrahens scapulae_, _transverso-scapularis minor_ and _tertius_, _interscapularis_ and _subscapularis_.

B. _VENTRAL MUSCLES OF THE SHOULDER (PECTORAL MUSCLES)_

These arise from the sternum or shoulder-girdle and are inserted
either into the humerus or into the radio-ulnar.

*52.* _M. pectoralis_ (Fig. 72).

This is placed on the ventral surface of the shoulder-girdle and consists of the following parts:

(α) _Portio sternalis anterior_ (Ecker), (Figs. 72, 73 _p_′).

*Dugès*, clavi-huméral, n. 70 (port. clavic. du grand pectoral).

This is the anterior portion of the _m. pectoralis_, it arises from the sternum proper and the epicoracoids. Broad at the origin, it becomes narrower as it runs outwards into a tendon attached to the _crista deltoidea humeri_.

(β) _Portio sternalis posterior_ (Ecker), (Figs. 72, 73 _p_″).

*Dugès*, sterno-huméral, n. 71 (port. sternal du grand
pectoral).--*Klein*, _humero-sternalis_.

This muscle is placed immediately behind the _portio sternalis anterior_, it has a somewhat broad origin from the sternum and xiphisternum; the muscle runs outwards and slightly forwards to be inserted into the groove beside the _crista deltoidea humeri_. The tendon of the _m. sterno-radialis_ passes between these two portions of the _m. pectoralis_.

(γ) _Portio abdominalis_ (Figs. 72, 73 _p_‴).

*Dugès*, abdomino-huméral, n. 69 (port. costal du grand
pectoral).--*Zenker*, _brachio-abdominalis_.--*Klein*,
_humero-abdominalis_.

Muscles of the chest, throat, and belly of _Rana esculenta_.

_ch_ M. coraco-humeralis.
_d_ M. deltoideus.
_oi_ M. obliquus abdom. internus.
_oe_ M. obliq. abdom. externus.
_oe_′ Scapular portion of same.
_oh_ M. omohyoideus.
_p_′ Port. sternalis anterior to m. pectoralis.
_p_″ Port. sternalis posterior to same.
_p_‴ Port. abdominalis of same.
_r_ M. rectus abdominis.
_r_′ Inner portion of same.
_sh_ M. sternohyoideus.
_sm_ M. submaxillaris.
_sm_′ Hyoid origin of same.
_sr_ M. sternoradialis.
]

This portion represents that part of _m. pectoralis major_ of human anatomy which arises from the costal cartilages, and more particularly that part which is connected with the aponeurosis of the _m. obliquus abdominis externus_. The muscle arises (1) from the _m. rectus abdominis_ (Fig. 72 _r_), that is, it forms a direct continuation of the outer portion of this muscle; (2) the inner, smaller part arises from the superficial surface of the aponeurosis of the _m. obliquus abdominis_. The muscle becomes narrower as it courses outwards and forwards, the outer fibres being longer and more oblique than the inner. The action of this muscle will necessarily vary according to the part or parts which are brought into action; speaking generally, the anterior extremities will be drawn downwards and towards each other.

*53.* _M. coraco-humeralis_ (Dugès), (Figs. 72, 73 _c.h._).

*Dugès*, n. 72.--*Klein*, _adductor humeri_.

A long, narrow muscle, lying upon the posterior border of the coracoid and the lowest part of the _m. subscapularis_. By its position it corresponds most nearly with the _m. pectoralis minor_, although its insertion does not. It has a narrow origin from the coracoid near the sternum, whence it courses outwards, under cover of the _port. sternalis anterior_ and _posterior_ of the _m. pectoralis_, to be inserted into the middle of the humerus between the deltoid and internal head of the triceps. It draws the limb towards the trunk.

*54.* _M. sternoradialis_ (Cuvier), (Figs. 72, 73 _s.r._).

*Dugès*, pré-sterno-clavi-radial, n. 74.

This muscle evidently represents the biceps of man, it lies in front of the _portio sternalis anterior_ of the _m. pectoralis_, its hinder border being under cover of the latter muscle. It takes origin from the episternum, omosternum, and the epicoracoid; from this broad origin the fibres converge while coursing backwards and outwards to be attached to a strong tendon. This tendon plays in a groove along the _crista deltoidea_, and is held in position by tendinous bands arising from the insertion of the _m. pectoralis_; it then pierces the lower portion of the muscular belly of the deltoid, and is inserted into the anterior extremity of the radial side of the radio-ulnar. The muscle is a powerful flexor of the forearm.

*55.* _M. deltoideus_ (Figs. 70, 72, 73 _d_).

*Dugès*, pré-sterno-scapulo-huméral, n. 68.

It is placed in front of and external to the _m. sternoradialis_, and represents both the _m. deltoideus_ and _supraspinatus_ of man. The muscle has two points of origin:--

(*a*) _Portio scapularis_, the larger, external portion is attached to the outer end of the clavicle, and to the anterior process of the precoracoid, but it arises chiefly from the dorsal surface of the scapula (from the same ridge as the _m. subscapularis_), and lastly from the anterior border and ventral surface of the scapula. The fibres pass outwards over the shoulder-joint.

Muscle of right shoulder and upper arm. The coracoids (_c.o._) and the clavicles (_cl_) have been drawn asunder after cutting through the sternum.

_c.h._ M. coraco-humeralis.
_cl_ Clavicle.
_c.o._ Coracoid.
_d_ M. deltoideus.
_d_′ Clavicular portion of m. deltoideus.
_i_ M. infraspinatus.
_i.s._ M. interscapularis.
_l.a._ M. levator anguli scapulae.
_l.d._ M. latissimus dorsi.
_p_′ Sternal portion of m. deltoideus.
_p_″ Anterior sternal portion of the m. pectoralis.
_p_‴ Posterior sternal portion of the m. pectoralis.
_s_ Scapula.
_s.r._ M. sternoradialis.
_t.r._ M. triceps brachii.
]

(*b*) _Pars clavicularis_ (_musc. cleido-humeralis_, Klein) arises from the inner extremity of the clavicle and from the omosternum and joins the _portio scapularis_.

The muscle is inserted into the humerus, the under part of the _portio scapularis_ being attached to the upper portion of the _crista deltoidea_; the outer fibres of this part, together with those of the _pars clavicularis_, are attached to the extremity of the _crista deltoidea_ and to the inner surface of the humerus as far as the distal extremity; just before its insertion the muscle is pierced by the tendon of the _m. sternoradialis_. The deltoid draws the limb forwards.

II. MUSCLES OF THE FORE-LIMB.

A. _MUSCLES OF THE ARM._

_M. sternoradialis (biceps)._ See page 82.

*56.* _M. triceps brachii_ (Fig. 73 _t.r._).

*Dugès*, scapulo-huméro-olecranien, n. 75.--*Capes*, *Zenker*, _m.
anconaeus_.

This muscle lies on the upper or dorsal surface of the arm, and has relations similar to those of the corresponding muscle in man. The long head arises from the posterior border of the scapula at the upper border of the glenoid cavity, and is here attached to the capsule of the joint; the inner head arises from the upper and inner surfaces of the anterior half of the humerus as far as the extremity; the outer head arises from the outer surface of the humerus. Additional fibres, which may be regarded as a fourth origin (_m. subanconaeus_), arise from the upper surface of the hinder half of the humerus. The fibres from these several origins unite to form a strong muscle, which covers the upper, inner, and outer surfaces of the bone, and then passes into a tendon. This tendon is attached to the capsule of the elbow-joint and inserted into the proximal extremity of the radio-ulnar. A cartilage, representing the olecranon, is found in the capsule at the point of attachment of the tendon.

B. _MUSCLES OF THE FOREARM._

(I.) Muscles of the flexor surface.