88 VERTEBRA OF SERPENTS. 



hypapophysis : this, in the python, is articulated by suture 

 to the neurapophyses ; it also presents a concave articular 

 surface anteriorly for the lower part of the basioccipital 

 tubercle, and a similar surface behind for the detached 

 central part of the body of the atlas, or " odontoid pro- 

 cess of the axis." The base of each neurapophysis has 

 an antero-internal articular surface for the exoccipital 

 tubercle, the middle one for the hyapophysis, and a 

 postero-internal surface for the upper and lateral parts of 

 the odontoid ; they thus rest on both the separated parts 

 of their proper centrum. The neurapophyses expand 

 and arch over the neural canal, but meet without coalesc- 

 ing. There is no neural spine. Each neurapophysis de- 

 velops from its upper and hinder border a short zyga- 

 pophysis, and from its side a still shorter diapophysis. 

 In the second vertebra, the odontoid presents a convex 

 tubercle anteriorly, which fills up the articular cavity in 

 the atlas for the occipital tubercle ; below this is the sur- 

 face for the hypapophysial part of the atlas, and above 

 and behind it are the two surfaces for the atlantal neura- 

 pophyses. The whole posterior surface of the odontoid 

 is anchylosed to the proper centrum of the axis, and in 

 part to its hypapophysis. The neural arch of the axis 

 develops a short ribless diapophysis from each side of 

 its base ; a thick sub-bifid zygapophysis from each side of 

 the posterior margin ; and a moderately long bent-back 

 spine from its upper part. The centrum terminates in a 

 ball behind, and below this sends downwards and back- 

 wards a long hyapophysis. 



At the opposite extreme of the elongated body, two or 

 three much simplified vertebras are usually found blended 

 together. In true serpents there are no scapular arch and 

 appendages, no sternum, no sacrum ; but a pair of slender 



