REPTILES 



229 



the way in which the internal organs are packed into the long 

 but narrow space available for the purpose. 



The skull is made up of very hard and polished bones, 

 its most notable features being the loose union between the 

 various bones connected with the jaws. The two halves of the 

 lower jaw, for instance, are not firmly united at their tip, as is 

 the case of most reptiles, but are only connected by an elastic 

 ligament which permits of a good deal of stretching. Not only 

 so, but the upper jaw also is 

 capable of a good deal of move- 

 ment. This flexibility has to do 

 with the necessity for great ex- 

 pansion in the act of swallowing 

 large prey, and also plays a large 

 part in enabling poisonous forms 

 to use their poison -fangs effec- 

 tively. It may also be noticed 

 that the hyoid apparatus is ex- 

 tremely small. The long back- 

 bone is made up of some two 

 or three hundred vertebrae, the 

 centra of which have the usual 

 reptilian shape, i.e. concave in 

 front and convex behind. Such 

 a large number of ball-and- 

 socket joints give a very large 

 amount of flexibility, but some 

 provision is necessary to impose 

 a limit to this, as otherwise dis- 

 location would be liable to occur 

 when complicated curvings were 



described This is 



' ' ' 



PANCREAS- 



Fig. 144. Structure of a Snake 



A, General dissection. B, Upper side of brain, c, Dia- 

 grammatic vertical section to show tear-chamber in front 



, , i - 



provided for by overlapping 



articular processes on the arches of the vertebrae, as in most 

 Vertebrates with well-ossified backbones (see p. 26), but in addition 

 to these a pair of wedge-shaped projections stick out from the 

 front of each arch and fit into corresponding pits at the back 

 of the preceding one. It should be mentioned that similar 

 processes are found in some other reptiles, as, for example, 

 Iguanas, where, however, they are not so well developed. 



