ANATOMY OF VERTEBRATES. 



173 



107 



metacarpal : the last phalanx supporting a claw. The three 

 nnddle digits, //, ///, in, have each tln-ce long phalanges, tlie 

 last heing 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 lias one metacarpal and two phalanges, the last supporting a 

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

 and no claw form the genus Homopiis, Dum. and Bilj. In 

 JSnnjs curopa-a, fig. 51, T, u, the first and fifth digits have each a 

 metacarpal and two phalanges ; the others have three plialanges ; 

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

 the poUex has two phalanges, the 

 second with a claw ; the three middle 

 digits have each three j)halanges, 

 l)ut only the index and medius liave 

 the claw ; the fifth digit has two 

 2>halangcs and no claw, whence 

 the generic name Triovi/x, proposed 

 for these frequenters of the nuiddy 

 estuary. 



In the Crocodilia the scai)ular 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 Ijone, arc 

 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 tlic coracoid 

 joins the lateral border of the ster- 

 num. TJiere is no trace of clavicle, 

 no acromial projection from the sca- 

 pula. 



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

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

 up(3n the short, obtuse, angular prominence, answering to the inner 

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

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

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



Bonos of rorc-arm and paGdle, Chclvnc. cli. 



