Part 102

a, Extensor carpi radialis; b, extensor digiti tertii; c, common or anterior digital extensor; d, extensor digiti quarti; e, flexor carpi externus; f, extensor carpi obliquus; f′, ulnar head of flexor carpi medius; g, brachialis; h, interosseus medius or suspensory ligament; i, flexor tendons; i′, branch of h, to superficial flexor tendon; 8, olecranon; 11, accessory carpal bone; 12′, metacarpal tuberosity. (After Ellenberger-Baum, Anat. für Künstler.) ]

FIG. 214.—MUSCLES OF ANTIBRACHIUM AND MANUS OF OX, INTERNAL VIEW.

a, Extensor carpi radialis; b, tendon of extensor digiti tertii; f, tendon of extensor carpi obliquus; g, brachialis; h, interosseus medius or suspensory ligament; i, flexor tendons; i′, branch of h; k, flexor carpi internus; l, flexor carpi medius; m, superficial digital flexor. (After Ellenberger-Baum, Anat. für Künstler.) ]

The internal head of the =triceps= is more developed than in the horse.

The =tensor fasciæ antibrachii= is a slender muscle.

IV. MUSCLES OF THE FOREARM

A. EXTENSOR DIVISION

The =extensor carpi radialis= is like that of the horse. There is sometimes a small muscle lying along its inner border, which may represent the extensores pollicis.

There are three =digital extensors=: 1. The =common= or =anterior digital extensor= (M. extensor digitalis communis) arises by two heads from the extensor epicondyle and the ulna. The heads fuse about the middle of the forearm, and terminate soon on a tendon which passes over the carpus and metacarpus, gradually inclining forward. At the fetlock joint it divides into two branches, which are inserted into the third phalanges. 2. The =internal digital extensor= (M. extensor digiti tertii proprius) arises on the extensor epicondyle, and is inserted by two branches into the second and third phalanges of the inner digit. The tendon receives two reinforcing slips from the suspensory ligament. 3. The =lateral digital extensor= (M. extensor digitalis lateralis s. digiti quarti proprius) arises from the external lateral ligament of the elbow joint, the external tuberosity of the radius, and the ulna. The tendon terminates like that of the preceding muscle.

FIG. 215.—RIGHT CARPUS OF OX WITH BURSÆ AND SYNOVIAL SHEATHS INJECTED, EXTERNAL VIEW. ]

FIG. 216.—RIGHT CARPUS OF OX WITH BURSÆ AND SYNOVIAL SHEATHS INJECTED, INTERNAL VIEW.

1, Extensor carpi radialis, with synovial sheath (1′) and bursa (1″); 2, extensor carpi obliquus, with synovial sheath (2′) and bursa (2″); 3, extensor digiti tertii proprius; 4, extensor digitalis communis; 3′, common synovial sheath of 3 and 4; 5, extensor digiti quarti proprius, with synovial sheath (5′); 6, 6′, flexor carpi externus, with bursa (6″); 7, flexor carpi internus, with synovial sheath; 8, deep digital flexor, with synovial sheath (8′); 9, flexor carpi medius; 10, superficial digital flexor, with synovial sheath 10′; a, radius; b, carpus; c, metacarpus; d, cut edge of annular ligament. (After Schmidtchen.) ]

The =extensor carpi obliquus= resembles that of the horse.

The extensor tendons are bound down at the carpus by an annular ligament, and are furnished with synovial sheaths (Figs. 215, 216).

B. FLEXOR DIVISION

The three =flexors of the carpus= are like those of the horse.

The =superficial digital flexor= is somewhat blended at its origin with the middle flexor of the carpus. It divides into two bellies, superficial and deep, terminating on tendons at the distal part of the forearm. The superficial tendon passes over the posterior annular ligament (Ligamentum carpi transversum), perforates the metacarpal fascia, and joins the deep tendon about the middle of the metacarpus. The deep belly is connected with the deep flexor by a strong fibrous band. Its tendon passes under the annular ligament in a groove on the deep flexor, from which it receives fibers. The conjoined tendon soon bifurcates, each branch receiving a reinforcing band from the suspensory ligament, and forming near the fetlock a ring for the corresponding branch of the deep flexor tendon. Passing under two digital annular ligaments, they are inserted into the volar surfaces of the second phalanges by three slips.

The =deep digital flexor= has the same heads as in the horse, the humeral head, as before mentioned, being connected with the deep portion of the superficial flexor. The tendon divides near the distal end of the metacarpus into two branches which are inserted into the volar surfaces of the third phalanges.

The synovial sheaths at the carpus present the following special features: One is found in connection with the tendon of the superficial part of the superficial flexor of the digits. There is a common sheath for the tendons of the common extensor and the inner extensor.

Bursæ may occur under the tendons of the proper extensors of the digits at the fetlock; they are constant only in old animals (Schmidtchen). The branches of the tendon of the common extensor are provided with synovial sheaths from their origin to the middle of the second phalanx. There are two digital synovial sheaths for the flexor tendons; they may communicate at their upper part, and extend from the distal third of the metacarpus nearly to the distal sesamoids. Bursæ occur between the latter and the branches of the deep flexor tendon.

METACARPAL MUSCLES

The =lumbricales= are absent, unless we regard as such the muscular bundles which arise on the deep flexor and are inserted into the superficial flexor tendon at the carpus.

The =interosseus medius= or suspensory ligament is somewhat more muscular than in the horse; indeed, in the young subject it may be almost entirely fleshy. Its arrangement is somewhat complex. Single at its origin, it detaches about the middle of the metacarpus a band which joins the tendon of the superficial flexor and concurs near the fetlock in the formation of the ring for the deep flexor tendon. A little lower down it divides into three and then into five branches. The lateral branches (two pairs) are attached to the corresponding sesamoids and tendons of the proper extensors, while the middle branch passes through the sulcus at the distal end of the metacarpus and bifurcates, each division fusing with the tendon of the corresponding proper extensor.

FIG. 217.—CROSS-SECTION OF DISTAL THIRD OF METACARPUS OF OX.

b, Tendon of extensor digiti tertii; c, tendon of common extensor; d, tendon of extensor digiti quarti; h, interosseus medius or suspensory ligament; i, tendons of digital flexors; i′, branch of h; 12, metacarpal bone. (After Ellenberger-Baum, Anat. für Künstler.) ]

It is to be noted that the fascia on the posterior face of the metacarpus and digit is very thick. It is continuous above with the ligamentum carpi transversum, and is attached on either side to the metacarpal bone. At the fetlock it forms the fibrous basis for the small claws, and below this it detaches two strong bands which diverge to be inserted into the second and third phalanges, blending with the lateral ligaments.

THE MUSCLES OF THE PELVIC LIMB

I. THE SUBLUMBAR MUSCLES