MUSCLES OF THE ARM— MUSCLES OF THE FOREARM AND MANUS 363 



The subscapularis is very broad at its upper part. It extends posteriorly up 

 to the dorsal angle of the scapula, but anteriorly only about two-thirds of the way 

 up to the vertebral border. 



The teres major presents nothing remarkable. 



The coraco-brachialis is short, wide, and undivided. There is a bursa between 

 its broad tendon of origin and the tendon of insertion of the subscapularis. 



The capsularis is variable; it may be half an inch wide or very small and 

 is frequently absent. 



MUSCLES OF THE ARM 



The biceps brachii is fusiform and not greatly developed. Its tendon of origin 

 is rounded and the underlying bursa communicates so freely with the shoulder joint 

 as to be regarded as an evagination of the synovial membrane of the latter. A small 

 band binds down the tendon in the bicipital groove. The tendon of insertion di- 

 vides into two branches. One branch passes back across the medial surface of the 

 neck of the radius to end on the proximal extremity of the ulna. The other is 

 attached to the rachus under cover of the brachialis tendon. 



The brachialis is large. Its tendon of insertion divides. The small branch is 

 inserted into the medial border of the radius distal to the biceps tendon. The large 

 branch crosses the mecUal border of the radius and ends on the medial surface of the 

 ulna distal to the biceps tendon; there is a bursa under this tendon. 



The tensor fasciae antibrachii resembles that of the horse, but is very wide and 

 bends around the posterior border of the triceps. 



The long head of the triceps is inserted into the summit of the olecranon by two 

 tendons, between wtich there is a synovial bursa. The lateral head is inserted into 

 a crest on the lateral surface of the olecranon by a thin tendon, under which there 

 is a bursa. The medial head arises from the proximal third of the medial surface 

 of the humerus; it is inserted into the medial surface of the olecranon by a short 

 tendon, under which there is a small bursa. 



There are two anconei. 



MUSCLES OF THE FOREARM AND MANUS 



The extensor carpi radialis is a strong, fleshy muscle, the tendon of which is 

 inserted into the proximal end of the third metacarpal bone. It may be divided 

 into two parts (M. extensor carpi radialis longus, brevis). 



The extensor carpi obliquus is well developed; it arises from the distal two-thirds 

 of the lateral surface of the radius and ulna and ends on the second metacarpal bone. 



The common digital extensor (M. extensor digitalis communis) arises on the 

 lateral epicondyle of the humerus and the lateral ligament of the elbow, and divides 

 into three parts. The tendon of the medial head ends chiefly on the third digit, 

 but commonly sends a small branch to the second. The tendon of the middle head 

 divides lower down into two branches for the third and fourth (chief) digits; above 

 this bifurcation it detaches a small branch to the second digit, which usually unites 

 with the tendon of the extensor digiti secundi. The tendon of the deep head di- 

 vides into two branches, the medial one joining the tendon of the middle head, while 

 the lateral one ends on the fifth digit. 



The extensor of the second digit (M. extensor digiti secundi proprius) is covered 

 by the preceding muscle, with which it is partially fuseil. It arises on the ulna. 

 Its delicate tendon usually unites with the tendon of the middle head of the common 

 extensor which goes to the second digit. 



The lateral digital extensor (M. extensor digitalis lateralis) consists of two dis- 

 tinct parts: (1) The large dorsal muscle is the extensor digiti quarti proprius; it 

 has a long tendon which ends on the fourth digit, and often sends a slip to the fifth 



