VERTEBRA OF SERPENTS. 87 



tenou-and-mortise in carpentry. In the caudal vertebrae, 

 the hypapophysis is double, the transition being effected 

 by its progressive bifurcation in the posterior abdominal 

 vertebrae. The diapophj^ses become much longer in the 

 caudal vertebroe, and support in the anterior ones short 

 ribs which usually become anchylosed to their extremi- 

 ties. 



The pleurapophyses or vertebral ribs in serpents have 

 an oblong articular surface, concave above and almost flat 

 below in the python, with a tubercle developed from the 

 upper part, and a rough surface excavated on the fore 

 part of the expanded head for the insertion of the pre- 

 costal ligament. They have a large medullary cavity, 

 with dense but thin walls, and a fine cancellous structure 

 at their articular ends. Their lower end supports a short 

 cartilaginous h^emapophysis, which is attached to the 

 broad and stiff abdominal scute. These scutes, alternately 

 raised and depressed by muscles attached to the ribs and 

 integument, aid in the gliding movements of serpents ; 

 and the ribs, like the legs in the centipede, subserve loco- 

 motion ; but they have also accessory functions in relation 

 to breathing and constriction. The anterior ribs in the 

 cobra (Fig. 13), pl^ are unusually long, and are slightly 

 bent ; they can be folded back one upon another, and can 

 be drawn forward, or erected, when they sustain a fold of 

 , integument, peculiarly colored in some species — e. g. the 

 spectacled cobra — and which has the effect of making 

 this venomous snake more conspicuous at the moment 

 when it is about to inflict its deadly bite. The ribs com- 

 mence in the cobra, as in other serpents, at the third ver- 

 tebra from the head. 



The centrum of the first vertebra coalesces with that 

 of the second, and its place is taken by an autogenous 



