Part 101

These resemble those of the horse; the coccygeus is, however, much more developed.

ABDOMINAL MUSCLES

The =obliquus abdominis externus= is somewhat thinner and has a less extensive origin, which begins at the lower part of the fifth intercostal space and ends on the last rib above its middle. The direction of the fibers in the flank is horizontal, and they do not reach to the external angle of the ilium, nor as high as the lumbar transverse processes. (In this region the abdominal tunic has a strong attachment to the point of the hip and the lumbo-dorsal fascia.) The aponeurosis is intimately united with the abdominal tunic, and does not detach a layer on the inner surface of the thigh.

FIG. 211.—DEEPER MUSCLES OF NECK, SHOULDER, AND THORAX OF OX.

c′, Cleido-occipitalis muscle; d, sterno-cephalicus; f, f′, long and external heads of triceps; g, superficial pectoral muscle; h, h′, posterior and anterior deep pectoral muscles; i, i′, serratus magnus; k, latissimus dorsi; l, obliquus abdominis externus; v′, biceps brachii; w, splenius; x, rhomboideus; y, trachelo-mastoideus; z, supraspinatus; z′, infraspinatus; z″, tendon of insertion of z′; 1′, cartilage of scapula; 2, tuberosity of spine of scapula; 3, acromion; 5, external tuberosity of humerus; 6, deltoid tuberosity; 8, olecranon; 26, transverse processes of cervical vertebræ; 27, posterior auricular muscles; X, wing of atlas. (After Ellenberger-Baum, Anat. für Künstler.) ]

The =obliquus abdominis internus= is more developed and has an additional origin from the lumbo-dorsal fascia. The aponeurosis blends with that of the external oblique near the linea alba, and detaches a layer which assists in the formation of the internal sheath of the rectus.

The =rectus abdominis= arises on the lateral border of the sternum as far forward as the third costal cartilage. The two muscles are separated, except near the pelvis, by an interval varying from two to four inches (ca. 5 to 10 cm.), so that this part of the abdominal wall is entirely fibrous. (The umbilicus is in a transverse plane through the third lumbar vertebra.) There are five tendinous inscriptions, on the third of which is a foramen for the passage of the subcutaneous abdominal vein (milk vein). The prepubic tendon has, in addition to branches inserted into the ilio-pectineal eminences, a strong attachment to the median common tendon of the adductors of the thigh, so that the abdominal wall is strongly retracted and almost vertical at its junction with the pelvis.

The =transversus abdominis= presents no striking differential features. The transversalis fascia is strong and distinct except over the diaphragm.

MUSCLES OF THE THORACIC LIMB

I. MUSCLES OF THE SHOULDER GIRDLE

The =trapezius= is much thicker and broader than in the horse, and is undivided. It arises on the ligamentum nuchæ and supraspinous ligament, from the atlas to the twelfth thoracic vertebra.

The =omo-transversarius= is a muscle (not present in the horse) which arises on the wing of the atlas, and, inconstantly, the transverse process of the second cervical vertebra, and is inserted into the scapular spine and fascia.

The =rhomboideus= is clearly divided into cervical and dorsal portions, the latter extending further than in the horse.

The =latissimus dorsi= has a broad tendon of origin, which blends with the lumbo-dorsal fascia; it is also attached to the eleventh and twelfth ribs, the fascia over the external intercostal and oblique abdominal muscles, and by a tendinous slip to the deep pectoral muscle.

The =mastoido-humeralis= has two distinct parts. The dorsal division (M. cleido-occipitalis) arises on the occipital bone and the ligamentum nuchæ. The ventral part (M. cleido-mastoideus) is smaller and arises by a round tendon on the mastoid process and the rectus capitis anterior major, and by a thin tendon on the mandible. At the shoulder a small muscle which arises on the first rib blends with the deep face of the mastoido-humeralis.

The =superficial pectoral= muscle does not present any striking difference.

The =deep pectoral= arises as far forward as the second rib and is undivided. However, the scapular portion may be considered to be represented by a small branch extending over the lower part of the supraspinatus. A tendon is detached from the dorsal edge, which blends with the latissimus dorsi and coraco-brachialis.

The =serratus magnus= is clearly divided into cervical and thoracic portions. The former is large and extends from the third (or second) cervical vertebra to the fifth rib, being overlapped behind by the thoracic part. The thoracic part is relatively thin and is covered by a very strong aponeurosis; it is attached to the fourth to the ninth ribs by six digitations, and is inserted by a flat tendon into the inner face of the dorsal angle of the scapula.

II. MUSCLES OF THE SHOULDER

The =deltoid= is clearly divided into acromial and scapular portions. The former arises on the acromion, the latter on the posterior border of the scapula and the aponeurotic covering of the infraspinatus. The scapular part of the muscle is largely inserted into the fascia covering the triceps.

The =supraspinatus=, =infraspinatus=, and =teres minor= do not differ materially from those of the horse.

The =subscapularis= consists of three portions with a common tendon of insertion.

The =teres major= and =coraco-brachialis= resemble those of the horse.

III. MUSCLES OF THE ARM

The =biceps= is smaller and less tendinous, and is situated more internally than in the horse. The tendon of origin is flat, and is bound down in the bicipital groove by a fibrous band. (In the sheep the tendon is round and passes through the shoulder joint.)

FIG. 212.—MUSCLES OF ANTIBRACHIUM AND MANUS OF OX, ANTERIOR VIEW.

a, Extensor carpi radialis; b, extensor digiti tertii; c, extensor digitalis communis; d, extensor digiti quarti (tendon); f, extensor carpi obliquus; g, brachialis; 12′, metacarpal tuberosity. (After Ellenberger-Baum, Anat. für Künstler.) ]

FIG. 213.—MUSCLES OF ANTIBRACHIUM AND MANUS OF OX, EXTERNAL VIEW.