44 2 CROCODILIA CHAP. 



scales, which cover the whole body, have a hard, horny, water- 

 proof covering, but between them the skin is soft. Each scale of 

 the sides, belly, and tail, and especially those of the lower jaw, 

 shows a little dot or pit. At this spot the epidermis is not 

 cornified or thickened, and a nerve with sensory corpuscles ends 

 beneath the bottom of the pit. Sometimes these pits are filled 

 with debris of cells, and on the lower jaw, especially on the chin, 

 these organs, instead of forming pits, are raised into little wart- 

 like prominences. 



The scutes or dermal portions of the scales consist of 

 thickened, cutaneous connective tissue, and are more or less 

 extensively ossified, thus forming a proper dermal armour. In 

 most recent Crocodilia the armour is restricted to the back, 

 with occasional osseous plates on the throat, as in Osteolaemus ; 

 regular although thin ossifications in the ventral scutes occur in 

 the Caimans only. The Crocodile and Alligator skins of com- 

 merce consist entirely of the tanned cutis, minus the epidermis 

 and the horny coverings of the scutes. In some fossil genera 

 the ventral armour was extensively developed, especially in 

 Teleosaurus, in some genera to the exclusion of dorsal ossifications. 

 The armour of the recent forms consists, so far as the large scutes 

 are concerned, of a considerable number of scutes, which are 

 arranged in transverse rows, each row corresponding with one 

 skeletal segment of the trunk proper. Mostly there is a detached 

 cluster of scutes on the back of the neck. On the trunk some of 

 the scutes are larger and more crested than others, and form in 

 their totality a variable number of longitudinal rows. The 

 median pair is generally the most conspicuous on the back. 

 Some of the more lateral rows of keeled scutes converge more and 

 more towards the tail, the inner rows drop out imperceptibly, and 

 two lateral rows combine on the middle of the tail into an un- 

 paired series of vertical blades. These are no longer bony, but 

 show more strongly developed horny sheaths ; they are very 

 flexible, and transform the tail into an effective propelling organ. 



Most of the larger scutes and the upper surface of the bones 

 of the skull have a peculiar gnawed-out, almost honeycombed 

 appearance, as is usual wherever most of the cutis itself is trans- 

 formed into bone or co-ossifies with underlying bone, while the 

 uppermost layers and the horny layer of the epidermis are much 

 reduced and thinned out. 



