Muscles of the Chelonicoi Shoulder-girdle. 305 



two heads run together on the under side of the arm, to be inserted by 

 a single strong terete tendon into the uhia, near its proximal end. 



In most Chelonians this muscle (PI, 13, figs. 2, 6, o) is repre- 

 sented by two distinct muscles, the 31. coraco-ulnaris and 31. coraco 

 radiaiis ,• the former arising from the more distal part of the posterior 

 edge of the coracoid, being inserted into the ulna near the prox- 

 imal end ; the other arising from the medial half of the same edge of 

 the coracoid, being inserted into the radius and outer side of the 

 wrist, and sometimes running as far as to the thumb. In one genus 

 {Chelonia) the second part of the muscle is represented by only a 

 tendonous ribbon continued on from the outside of the loAver end of 

 the first, and inserted in the region of the wrist. 



There are two muscles remaining which have a scapular origin in 

 man, the " subscapularis," and the long head of the " triceps." 

 The area of origin for the "subscapularis" (PI. 12, fig. 2, s), covers 

 the anterior surface of the human sca])ula, its fibers converging tow^ard 

 the head of the humerus. Its insertion is into the lesser or ulnar 

 tuberosity (PI. 12, fig. 3,8). 



In the Chelonians this is represented by two more or less distinct 

 bundles {31. M. scapido-hurneralis secundus and tertius), arising from 

 the scapula and inserted into the internal (ulnar) tuberosity (PI. 13, 

 figs. 1 and 2, sa^ 8&). The area of their origin covers the greater 

 part of the shaft of the scapula from the origin of the "teres major" 

 (PI. 13, fig. 1, i), extending around in front and on the posterior side 

 quite to the inner side 'of the shaft. On account of the small size of 

 the shaft, the origin, ends, and body of these muscles are pretty well 

 fused together, but toward their distal ends two bundles may, in 

 some cases, be made out, and in Ptychemys^ of which the most care- 

 ful dissections were made, two distinct insertions were made out, 

 one on the outer, the other on the inner side of the ulnar — that is the 

 greater, or internal, tuberosity (PI. 13, figs. 3 and 4, sa, 8&). The lower 

 part of the insertion of the 31. coraeo-hwi/endis prinms, — the repre- 

 sentative of the " coraco-brachialis " (figs. 3 and 4, 7), se})anites these 

 areas. 



From the rim of the glenoid cavity on the outer side, at the base of 

 the scapula (PI. 13, fig. 1, ii«), arises, by a tendon, a muscle which is 

 joined by a stronger bundle, having a humeral origin, and Avhich it 

 overlies for its whole length. It is inserted into the proximal head of 

 the ulna, on its dorsal side, and acts as an extensor of the forearm, 

 I presume there will be no hesitancy in regarding this as the repre- 

 sentative of the long head of the " triceps " of anthropotomy. 



