ANATOMY OF VEETEBRATES. 



187 



117 



shaft is almost straight, slightly expanded at the distal end, at the 

 back part of which the condyles are feebly indicated. In Terra- 

 penes, fig. 51, w, and Tortoises, the femur equals or exceeds the 

 humerus in length : its shaft is more bent : the trochanter is divided 

 into two processes, most distinct in Trionyx. In no Chelonian is 

 there a medullary cavity : ossification extends throughout the bone : 

 the two bones of the leg, ib. x, Y, are nearly straight ; the tibia is the 

 largest, with the proximal end almost semi- 

 circular, and the distal one less expanded 

 and subconcave, with a slightly-developed 

 malleolus in Testudo and Emys. The fibula, 

 fig. 117, 67, is a little bent, enlarging the 

 interosseous space in Trionyx: it presents 

 a convexity to the tarsus. There is no bony 

 patella in any Chelonian. In Testudo 

 tabulata I found a synovial joint between 

 its fibrous representative and the femur, 

 distinct from the proper capsule of the knee- 

 joint. The proximal row of the tarsus con- 

 sists of two bones, astragalus, a, and cal- 

 caneum, which in most Tortoises become 

 confluent. The distal row consists of five 

 bones, four of which support the four nor- 

 mal toes, and the fifth a rudiment of the 

 metatarsal of the fifth toe, v ; the fourth 

 and fifth of the second row of tarsals 

 answer to the os cuboides of higher ani- 

 mals ; the other three bones to the three 

 ossa cuneiformia. The astragalar part of 

 the single proximal bone includes also the naviculare. 



In the Trionyx, fig. 117, the proximal row consists of a single 

 bone, a, answering to the astragalus and naviculare : the distal 

 row consists of five bones, of which the three cuneiformia are very 

 small : the two divisions of the cuboides, h', c, are very large ; 

 the first may include the articular part of the calcaneum ; the 

 outermost is dilated and angular. In Clielone and Chelys the 

 calcaneum is distinct from both the cuboid and the astragalo-navi- 

 cular bones. The digits are moderately long, rather flattened and 

 divaricated, supporting the hind webbed foot ; the metatarsal sup- 

 ports two phalanges in the first toe ; in the other toes it supports 

 three, the last having a claw. 



In Trionyx the fifth digit, fig. 117, v, has two small phalanges 

 and no claw. In Emys and Cistudo the digits decrease in strength 



Bones of leg and foot, 

 Trionyx. en. 



