480 University of California Publications in Zoology [Vol. 13 



mesio-caudal surface of the olecranon process of the ulna {fix. car. 

 ul., pi. 39), and is inserted into the tip of the pisiform bone. The 

 length of the latter gives the muscle a strong leverage and makes 

 it a very powerful flexor of the manus. 



37. Flexor digitorum sublimis {fix. dig. sub., fig. T) arises from 

 the common flexor tendon and the adjacent part of the mesial 

 surface of the ulna, and passes distad beneath the palmaris. In 

 the distal third of the forearm it ends in four tendons which pass 

 beneath the bony arch formed by the falciform and pisiform bones, 

 and are inserted into the bases of the second phalanges of digits 

 2, 3, 4, and 5 {fix. dig. sub., pi. 39). This muscle flexes first the 

 digits, and, by continued action, the manus. 



38. Flexor digitorum profundus {fix. dig. pro., fig. S) arises 

 by three heads. The largest head takes origin on the caudal and 

 mesial surfaces of the ulna from the base of the olecranon to the 

 middle of the bone {fix. dig. pro., pi. 39) ; this head is superficial 

 on the lateral side of the forearm. The second head arises by the 

 common flexor tendon from the mesial condyle of the humerus. 

 This part of the muscle is superficial on the mesial side of the fore- 

 arm {fix. dig. pro., fig. T). The third and smallest portion arises 

 from a narrow line along the proximal third of the ventro-mesial 

 border of the ulna. These three parts unite to form a common 

 tendon which passes through the annular ligament beneath the 

 tendons of the preceding muscle. The tendon then divides into five 

 parts which are inserted into the palmar surfaces of the bases of 

 the terminal phalanges of all five digits. This muscle is a stronger 

 flexor of the digits and manus than the flexor digitorum sublimis. 



39. Flexor carpi radialis {fix. car. ra., fig. T) arises from the 

 common flexor tendon and is inserted on the palmar surface of the 

 base of metacarpal 2. This is a deep muscle in the upper two- 

 thirds of the forearm. It is a flexor of the carpus. 



40. Pronator teres {pron. ter., figs. R, T) arises from the 

 internal condyle of the humerus and is inserted on the antero- 

 mesial surface of the radius near its middle {pron. ter., pi. 39). 

 It is probable that this muscle has little pronating action, but 

 serves rather as a flexor of the forearm. 



41. Supinator arises form the external condyle of the humerus 

 and is inserted on the proximal third of the cephalic surface of the 

 radius {sup., pi. 38). This muscle is probably homologous with 

 the muscle known as the braehioradialis in the cat. but it more 



