ANATOMY OF VERTEBRATES. 



173 



107 



metacarpal : the last phalanx supporting a claw. The three 

 middle digits, it, Hi, iv, have each three long phalanges, the 

 last being flattened and without a claw ; the fifth has two pha- 

 langes. All these are connected together by a web. In the 

 Tortoise, fig. 108, all the toes are very short and subequal ; and 

 each has one metacarpal and two phalanges, the last supporting a 

 claw ; the few species in which the fifth has but one phalanx 

 and no claw form the genus Homopus, Dum. and Bib. In 

 Emys europ&a, fig. 51, T, u, the first and fifth digits have each a 

 metacarpal and two phalanges ; the others have three phalanges ; 

 the last bears a claw in each digit. In the Soft or Mud-turtles. 



C5 



the pollex has two phalanges, the 

 second with a claw ; the three middle 

 digits have each three phalanges, 

 but only the index and meclius have 

 the claw; the fifth digit has two 



o 



phalanges and no claw, whence 

 the generic name Triomjx, proposed 

 for these frequenters of the muddy 

 estuary. 



In the Crocodilia the scapular arch 

 consists of a simple scapula, fig. 57, 

 51, and coracoid, ib. 52, and fig. 54, 

 8 : these compressed, narrow, mode- 

 rately long plates of bone, are 

 thickest where they are united to- 

 gether to form the glenoid cavity 

 for the humerus. In each, the bone 

 contracts beyond the articular ex- 

 pansion, becomes sub-cylindrical, 

 but soon again flattens and expands 

 to its opposite end ; that of the sca- 

 pula is free, that of the coracoid 

 joins the lateral border of the ster- 

 num. There is no trace of clavicle, 

 no acromial projection from the sca- 

 pula. 



The humerus, fig. 51, 53, presents two curves : the articular head 

 is a transversely elongated, sub-oval convexity ; it is continued 

 upon the short, obtuse, angular prominence, answering to the inner 

 or ulnar tuberosity. The radial crest begins to project from the 

 shaft at some distance from the head of the bone. There is a 

 longitudinal ridge on the anconal surface close to the radial border. 



Bones of fore-arm and paddle, Chelone. CLI. 



