TEGUMENTS OF REPTILES. 557 



femorales ' afford generic characters. They are wanting in the 

 Chameleons. Certain male Geckos have both femoral and sub- 

 anal pores. In Pygopus lepidopodus the subanal pores are dis- 

 posed in a single series, but in Lialis in pairs, on each side. 



In the Crocodilia the conversion of parts of the integument into 

 bone is constant, and the osseous structure shows interlaced or 

 crossing fibres, like that of the derm in and from which the 

 scutes are developed. The arrangements and forms of these 

 scutes in different genera of recent and fossil Crocodilia are 

 described at pp. 198, 199. As in Fishes, the dermoskeleton was 

 most developed in the extinct secondary species. In modern 

 Crocodiles a serrated crest extends above the tail, which divides 

 at the base of that oro-an. 



A section of the dorsal integument of Trionyx ferox shows a 

 thin epiderm, then a thicker layer of elastic fibres, next many 

 layers of fibres crossing each other regularly, and producing 

 seeming layers of the derm. In Sphargis a superficial portion of 

 the derm is ossified, so as to form a kind of girdle to the trunk, 

 beneath which is a felt of soft corium, and under this the endo- 

 skeleton. In all other Chelonia the derm adheres to the periosteum 

 of certain neural spines and pairs of pleur- and hsem-apophyses, 

 whence ossification extends in different degrees into the substance 

 of the derm. In most Chelonia a series of bones are developed 

 independently in the derm, at the circumference of the trunk, 

 and also above certain neural spines, with winch they may or 

 may not become anchylosed. 1 



The dermal bones connate with neural spines are those above 

 the nine dorsal vertebrae, figs. 370, 371, ck, si-ss : they are 

 termed ' neural plates.' The dermal bones connate with pleura- 

 pophyses are those which take ossification from near the heads of 

 the second to the ninth, inclusive of the dorsal ribs, ib. ph-ph. 

 The dermal bones connate with hremapophyses are those which 

 start from the sternal or abdominal ribs, or coalesced groups of 

 ribs, figs. 372, 373, called hyosternal, lis, hyposternal, ps, and 

 xiphisternal, xs. Occasionally, ossification extends into the skin 

 from the entosternal, s (Emyda ceylonensis), and from the epi- 

 sternals, es (Cryptopus Petersii). The dermal bones are least 

 developed in the Trionycidce, and are not covered by horny epi- 

 derm. e Neural ' and ' costal ' plates are present in all. One 

 pair of dermal bones is developed from the hyosternals in Trionyx 

 siibplanus', in Trionyx niloticus and some other species dermal 

 bones are developed from the hyo-, hypo- and xiphi-stcrnals, the 



1 clxii. p. 165. 



