ANATOMY OF VEKTEBRATES. 



187 



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

 back pai't of which the condyles are fceljly indicated. In Terra- 

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

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

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

 there a medullary cavity : ossification extends throughout the bone : 

 the two l)ones of the leg, ib. x, Y, are nearly straight ; the til)ia is the 

 largest, with the proximal end almost semi- 

 circular, and the distal one less expanded 

 and suljconcave, with a slightly-developed 

 malleolus in TesttuJo and Ennjs. Tlie fibula, 

 fig. 117, G7, is a little bent, enlarging the 

 interosseous space in Trionijx : it presents 

 a convexity to the tarsus. There is no bony 

 patella in any Chelonian. In Tuatudo 

 tdhnlata I found a synovial joint between 

 its fibrous representative and the femur, 

 distinct from the proper capsule of the knee- 

 joint. The piroximal row of the tarsus con- 

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

 caneum, which in most Tortoises liccome 

 contluent. 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 cidwides of higher ani- 

 mals ; the other three bones to the three 

 c>ssa cimeiformia. The astragalar part of 

 the single proximal bone includes also the naviculare. 



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

 ])one, a, answering to the astragalus and naviculare : the distal 

 row consists of five l>ones, of wliich 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 angidar. In Clidonc 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 weighed foot ; the metatarsal sup- 

 ports two jihalangcs 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 Einys and Cistudo the digits decrease in strength 



TliuVlJX. CLI. 



