XII 



PHYLUM CHORD ATA 



439 



The various regions of the 

 spinal column are well marked 

 in most of the Lizards, in the 

 Chelonia, and in the Croco- 

 dilia (Fig. 248). In the Snakes 

 and many of the snake-like 

 Lizards only two regions are 

 distinguishable pre - caudal 

 and caudal. In the others 

 there is a sacral region com- 

 prising two vertebrae, which 

 have strong transverse pro- 

 cesses for articulation with 

 the ilia. The first and second 

 vertebrae are always modified 

 to form an atlas and axis. 

 Ribs are developed in con- 

 nection with all the vertebrae 

 of the pre-sacral or pre-caudal 

 region ; in the caudal region 

 they are usually replaced by 

 inferior arches. In the Flying 

 Lizards (Draco] a number 

 of the ribs are greatly pro- 

 duced, and support a pair of 

 wide flaps of skin at the sides 

 of the body, acting as wings 

 or rather as parachutes. 

 In Hatteria and Crocodilia 

 each rib has connected 

 with it posteriorly a flattened 

 curved cartilage, the un- 

 cinate. 



