270 FROGS, TOADS, AND NEWTS [CH. VIII 



have the ball at the hinder end, and the socket at the 

 front end of the centrum, the eighth has a socket at each 

 end, while the ninth has a ball at the front and a split 

 knob at the back articulating with the urostyle. Further 

 connexion between the vertebrae is afforded by inter- 

 locking processes projecting forwards and backwards from 

 the dorsal region of the neural arches. Each vertebra, 

 except the atlas, has two pairs of such processes, one pair 

 anterior, the other posterior. The anterior pair of any 

 one vertebra is overlapped by the posterior pair of the 

 vertebra next in front. The surfaces of contact are smooth, 

 and in life are covered by smooth cartilage; they are 

 bound together by ligaments and, as in all moveable joints, 

 a fluid, termed synovial fluid, acts as a lubricant to prevent 

 friction. It will thus be seen that at the anterior end of 

 a vertebra the smooth facets of the interlocking processes 

 are directed dorsalwards, but at the posterior end ventral- 

 wards, and so the head- and tail-end of any isolated 

 vertebra can be readily determined. The axial skeleton 

 then performs two main functions, it is the main pillar 

 in the animal fabric, and it protects the central nervous 

 system on which depends the co-ordination of the entire 

 machine. 



The brain itself consists, beginning at the anterior 

 end, of the olfactory lobes, of the cerebral hemispheres, 

 the thalamencephalon, with the pineal body, infundibulum 

 and pituitary body, the optic lobes, the cerebellum and 

 the medulla oblongata (vide Fig. 46). The cerebral hemi- 

 spheres are the seat of origin of all spontaneous actions, 

 that is to say, actions not provoked reflexly by external 



