MUSCLES OF THE THORACIC LIMB 



373 



medial ligament of the elbow and under the ulnar tendon of the biceps and ends 

 just proximal to the latter. The tendon of the biceps forms a partial sheath for 

 that of the brachialis. 



The tensor fasciae antibrachii is thin and narrow. It arises on the tendon and 

 lateral surlace 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 medial head is very long; it arises from 

 a mark on the proximal fourth of the medial surface of 

 the humerus, just behind the insertion of the teres major 

 and latissimus dorsi. A bursa lies on the olecranon in 

 front of the common tendon of insertion. 



The brachioradialis is a long, narrow, delicate mus- 

 cle, situated superficially on the dorsal surface of the 

 forearm. It arises with the extensor carpi on the crest 

 above the lateral epicondyle of the humerus, and is in- 

 serted into the distal part of the medial border of the 

 radius. It is often much reduced, and is sometimes ab- 

 sent. It rotates the forearm and paw outward. 



The extensor carpi radialis arises on the lateral con- 

 dyloid crest and divides into two parts. The larger lat- 

 eral part, the extensor carpi radialis brevis, ends on the 

 proximal end of the third metacarpal bone. The medial 

 and more superficial part, the extensor carpi radialis 

 longus, ends on the second metacarpal bone. (A ten- 

 don to the fourth metacarpal may occur.) 



The extensor carpi obliquus or abductor poUicis 

 longus arises from the lateral border and dorsal surface 

 of the ulna, the interosseous ligament, and the proximal 

 part of the lateral border of the radius. It is inserted 

 into the first metacarpal bone by a tendon which con- 

 tains 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 digi- 

 talis communis) arises on the lateral epicondyle of the 

 humerus and the lateral ligament of the elbow joint. 

 It has four bellies, each of which has a tendon of inser- 

 tion. These end on 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 ex- 

 tensors. It arises on the proximal half of the ulna. Its 

 tendon descends with that of the common extensor and 

 divides into two branches. The delicate medial branch 

 ends on the first digit, while the larger lateral one ends 

 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 lateral epicondyle of the 

 humerus and the lateral ligament of the elbow joint. The larger superficial muscle 

 is the extensor of the third and fourth digits (M. extensor digiti tertii et quarti) ; 



Fig. 323. — Muscles of An-ttbr.4- 



CHIUM AXD :\IaNUS of DoGJ 



Lateral View. 



a, Triceps brachii; 6, brachi- 

 alis: c, extensor carpi radialis; d, 

 common digital extensor; d', d", 

 d'" , d"", tendons of preceding; e, 

 lateral digital extensor; e', /, ten- 

 dons of preceding; g, ulnaris 

 lateralis; A, ulnar head, h' , hu- 

 meral head of flexor carpi ulnaris; 

 i, extensor carpi obliquus (s. ab- 

 ductor pollicis longus) ; k, inter- 

 ossei; /, branches from preceding 

 to extensor tendons; 1, olecranon; 

 2, radius; 3, lateral epicondyle of 

 humerus. (After Ellenberger, in 

 Leisering's Atlas.) 



