172 



ANATOMY OF VERTEBRATES. 



106 



Tortoise (Testudo) it is shorter, in Chelys, fig. 106, b, it is longer 

 than the scapula, a. This bone in all Chelonians is a strong, straight 

 columnar one, with the upper end connected by ligament with the 

 inner surface of the first costal plate, fig. 51, N; it descends almost 

 vertically to the shoulder-joint, of which it forms, in common with 

 the coracoid, the 'glenoid' cavity, fig. 106, //. The coracoid, 

 suturally united at that end with the scapula, passes inward and 

 backward, fig. 51, o, expanding and becoming flattened at its 

 median end, which does not meet its fellow nor articulate with 

 the sternum. The coracoid is broad and short in the Tortoise ; 



long and slender in Chelone and 

 Emys, fig. 51, o, of intermediate 

 proportions in Trionyx and Chelys, 

 fig. 106, c. The scapular arch 

 and proximal part of the limb being 

 included in the thoracic abdominal 

 box, the humerus is peculiarly 

 bent and twisted in the terres- 

 trial species in order to emerge 

 from the front fissure, and plant 

 the foot on the ground, fig. 51, 

 p. In the Tortoise the ordinary 

 position of the fore-limb is that 

 of extreme pronation, with the 

 olecranon forward and outward, 

 and the radial side of the hand 

 downward. The capsule of the 

 shoulder-joint includes a consider- 

 able part of the neck of the 

 humerus. The hemispheroid 'head projects unusually from the 

 back part of the bone, which looks upward : the tuberosities 

 are large and bent toward the palmar aspect : that which is 

 internal in most animals is here ' postero-superior ; ' that called 

 ' external ' is 6 postero-internal ' in position ; from the former is 

 continued the ' deltoid crest.' The distal end is expanded and 

 rather flattened from before backward. In the Turtle the humeral 

 shaft and its lower end is compressed laterally : and the bone 

 is almost straight in those marine species ; in all Chelonia it is 

 solid throughout. The ulna is shorter, and in the Turtle, fig. 

 107, b, the olecranon is less developed than in the Tortoise, fig. 108, 

 by 55. The contrast between the marchers and the swimmers is 

 most striking in the proportions of the toes. In the Turtle, 

 fig. 107, the pollex, /, is short and has two phalanges after the 



Scapular arch, Chehjs. CLI. 



