250 THE ANATOMY OF VEETEBRATED ANIMALS. 



valve, or earlid, lies above eacli, and can be sbnt down 

 over it. All are partially aquatic in babit, and some (tbe 

 Gavials) are completely so. None of tbe existing genera 

 are marine, tboiigb many ancient Crocodilia inhabited tbe 

 sea. 



Tbe dermal armour is composed of scutes covered by 

 epidermic scales of corresponding form. When tbe armour 

 is complete — as in Caiman and Jacare alone among existing 

 Crocodilia, in Teleosaurus and Stagonolepis among extinct 

 fonns — it consists of transverse rows of quadrate bonyjDlates, 

 disposed so as to foiTu a distinct dorsal and ventral shield, 

 separated by soft integument, in tbe trunk, but united into 

 continuous rings on tbe tail. Tbe scutes of tbe same row 

 are united suttu-ally ; those of each row overlap their suc- 

 cessors, which present smooth facets to receive their under- 

 surfaces. In existing Crocodilia, in tbe extinct Crocodilus 

 Sastinc/sicB, and in Stagonolepis, each ventral scute consists 

 of two pieces, a small anterior and a large posterior, united 

 by a suture. The scutes always exhibit a pitted sculpture, 

 and those of the dorsal region are ridged longitudinally, 

 while tbe ventral scales are always flat. More or fewer 

 dorsal scutes exist in all crocodiles, and those upon tbe 

 neck sometimes form distinct " nuchal " and " cei-vical " 

 groups, distinct from the dorsal shield. The dorsal scutes 

 do not always overlap, and the ventral scutes are absent, or 

 incompletely ossified, in most existing Crocodilia. 



In these reptiles the vertebral column is always thoroughly 

 ossified, and mai'ked out into distinct cervical, dorsal, lumbar, 

 sacral, and caudal regions. Tbe number of the presacral ver- 

 tebrae is twenty -four ; that of the sacral, two, in all the recent 

 forms, and probably in the extinct genera also. The num- 

 ber of the caudal vertebrae varies, but is not less than 

 thirty-five. The number of the cervical, dorsal, and lum- 

 bar vertebrae varies ; but there are usually nine of the first, 

 eleven or twelve of the second, and four, or three, of the 

 third description. 



In existing Crocodilia all the vertebrae, except the atlas 

 and axis, the two sacrals, and the fii'st caudal, are procoelous. 



