478 University of California Publications in Zoology [Vol. 13 



a. Caput longum {bic, fig. T) in the gopher arises from the 

 upper margin of the glenoid cavity, and its tendon traverses the 

 capsule of the shoulder joint. 



b. Caput breve arises from the tip of the coracoid process of 

 the scapula in common with the origin of the coracobrachialis. 

 The two heads are separate nearly to their insertion, where they 

 unite to form a common tendon which is attached to the ventro- 

 mesial surface of the ulna and slightly to the radius, in common 

 with the tendon of the brachialis {bic, pi. 38, 39). The biceps is 

 the principal flexor of the forearm. 



26. Coracobrachialis (cor. br., fig. T) arises from the coracoid 

 process of the scapula and is inserted in a line along the mesial 

 surface of the humerus for its distal two-thirds {cor. br., pi. 39). 

 This muscle is small and is an unimportant adductor of the arm. 



27. Brachialis {bra., fig. S) consists of a large lateral portion 

 and a small mesial portion, the origins of which lie on either side 

 of the deltoid tuberosity. The lateral origin occupies the posterior 

 and lateral surfaces of the humerus for the proximal third of the 

 bone. The mesial part arises from the base of the deltoid tuberosity 

 {bra., pi. 38, 39). The two parts join near the middle of the humerus, 

 and are inserted on the ulna and radius in common with the biceps. 

 This muscle, especially the lateral part, is a strong flexor of the 

 forearm. 



28. Extensor carpi radialis longus {ex. car. ra. lo., figs. Q, R) 

 arises on the cephalic surface of the external supracondylar ridge of 

 the humerus, and is inserted on the dorsal surface of the base of the 

 second metacarpal {ex. car. ra. lo., pi. 38). 



29. Extensor carpi radialis brevis {ex. car. ra. br., figs. Q, R) 

 arises on the cephalic surface of the external supracondylar ridge of 

 the humerus just distal to the origin of 28, and is inserted on the 

 dorsal surface of the base of the third metacarpal {ex. car. ra. br., 

 pi. 38). This is a stronger muscle than the preceding; the action 

 of both muscles is to extend the manus and to render the carpal 

 articulation rigid. 



30. Abductor pollicis longus {ahd. pol. lo., fig. S) arises from 

 the lateral surface of the ulna in a curved line from the ulno- 

 humeral articulation to the middle of the bone {ahd. pol. lo., pi. 38). 

 This muscle occupies the deeply grooved lateral surface of the 

 ulna, passing beneath the greatly enlarged external collateral liga- 

 ment, and becomes superficial only in the distal third of the fore- 



