Part 111

The =deltoid= is clearly divided into scapular and acromial parts, the former arising on the spine, the latter on the acromion of the scapula. Both end on the deltoid tuberosity.

The =supraspinatus= ends chiefly on the external tuberosity of the humerus, but has a small attachment to the internal tuberosity also.

The =infraspinatus= is inserted into the outer surface of the external tuberosity of the humerus.

FIG. 232.—MUSCLES OF THORACIC LIMB OF DOG, INTERNAL VIEW. (Ellenberger-Baum, Anat. des Hundes.) ]

The =teres minor= arises on a tubercle on the posterior border of the scapula, just above the glenoid cavity, and is inserted into the deltoid ridge.

The =subscapularis= is wide and is somewhat multipennate in structure, being intersected by fibrous septa which are attached to the rough lines on the costal surface of the scapula.

The =teres major= is thick. It arises on the upper part of the posterior border of the scapula and on the subscapularis.

The =coraco-brachialis= is short and undivided, and is inserted into the upper part of the postero-internal surface of the humerus.

The capsularis is absent.

FIG. 233.—MUSCLES OF ANTIBRACHIUM AND MANUS OF DOG, EXTERNAL VIEW.

a, Triceps brachii; b, brachialis; c, extensor carpi radialis; d, common or anterior digital extensor; d′, d″, d‴, d⁗, tendons of preceding; e, lateral digital extensor; e′, f, tendons of preceding; g, extensor carpi ulnaris; h, h′, flexor carpi ulnaris; i, extensor carpi obliquus (s. abductor pollicis longus); k, interossei; l, branches from preceding to extensor tendons; 1, olecranon; 2, radius; 3, extensor epicondyle of humerus. (After Ellenberger, in Leisering’s Atlas.) ]

The =biceps brachii= lies almost entirely on the inner surface of the humerus. It is long and fusiform. The tendon of origin is round, and passes through the capsule of the shoulder joint. The tendon of insertion is bifid, one branch being attached to the ulnar, the other to the radial tuberosity.

The =brachialis= is very little curved, and is inserted chiefly into the tuberosity and inner border of the ulna.

The =tensor fasciæ antibrachii= is thin and narrow. It arises on the outer surface of the latissimus dorsi, and ends on the olecranon and the fascia of the forearm.

The =triceps= has an additional deep head (Caput accessorium), which arises just below the head of the humerus.

The =brachio-radialis= is a long, narrow, delicate muscle, situated superficially on the anterior surface of the forearm. It arises with the extensor carpi on the crest above the extensor epicondyle of the humerus, and is inserted into the distal part of the inner border of the radius. It is often much reduced, and is sometimes absent. It rotates the forearm and paw outward.

The =extensor carpi= divides into two parts. The larger outer part, the =extensor carpi radialis brevis=, ends on the proximal end of the third metacarpal bone. The inner and more superficial part, the =extensor carpi radialis longus=, ends on the second metacarpal bone. (A tendon to the fourth metacarpal may occur.)

The =extensor carpi obliquus= or =abductor pollicis longus= arises from the outer border and anterior surface of the ulna, the interosseous ligament, and the outer border of the radius. It is inserted into the first metacarpal bone by a tendon which contains a small (sesamoid?) bone. It abducts the first digit.

There are three (or four) =extensors of the digits=.

1. The =common digital extensor= (M. extensor digitalis communis) arises on the extensor epicondyle of the humerus and the lateral ligament of the elbow joint. It has four bellies, each terminating in a tendon. These are inserted into the third phalanges of the second, third, fourth, and fifth digits.

2. The =extensor of the first and second digits= (M. extensor pollicis longus et extensor indicis proprius) is small, and is covered by the common and lateral extensors. It arises on the proximal part of the ulna. Its tendon passes down with that of the common extensor and divides into two branches. The delicate inner branch ends on the first digit, while the other blends with the tendon of the common extensor for the second digit.

3. The =lateral digital extensor= (M. extensor digitalis lateralis) consists of two muscles which are not rarely fused. They arise on the extensor epicondyle of the humerus and the lateral ligament of the elbow joint. The larger, =superficial belly= (M. extensor digiti tertii et quarti) terminates on a tendon which divides at or near the carpus into two branches, which are inserted into the third phalanges of the third and fourth digits, blending with the corresponding tendons of the common extensor. The =posterior belly= (M. extensor digiti quinti) terminates by a tendon which fuses with that of the common extensor for the fifth digit.

The =ulnaris lateralis= or =extensor carpi ulnaris= corresponds to the flexor carpi externus of the horse, but is an extensor of the carpus. It is a large flat muscle which lies on the outer surface of the ulna. It arises on the extensor epicondyle of the humerus, and is inserted into the proximal end of the fifth metacarpal and the accessory carpal bone.

FIG. 234.—VOLAR MUSCLES OF FORE PAW OF DOG.

a, Abductor pollicis brevis et opponens pollicis; b, flexor pollicis brevis; c, adductor pollicis; d, adductor digiti secundi; e, adductor digiti quinti; f, flexor digiti quinti brevis; g, abductor digiti quinti; h, interossei; 1, accessory carpal bone; 2, first digit; 3–6, sesamoids of metacarpo-phalangeal joints. (Ellenberger-Baum, Anat. d. Hundes.) ]

The =ulnaris medialis= or =flexor carpi medius= (s. ulnaris) consists of two quite distinct heads. The larger, =humeral head= arises on the flexor epicondyle, while the smaller, superficial =ulnar head= arises on the posterior border of the ulna. The tendons of the two end together on the accessory carpal bone.

The =radialis volaris= or =flexor carpi internus= (s. radialis) arises on the flexor epicondyle of the humerus and is inserted by a bifid tendon into the second and third metacarpal bones.

The tendons of the foregoing muscles are provided with synovial sheaths at the carpus.