Vertebrae of Constricting Serpetit. 33 



Snake are described at p. 178. Briicke, Denkschrift. Kais. 

 Akad. Wiss. Wien. iii. p. 342^ 1852. 

 For the reproductive^ see Martin St. Ange, Etude de FAppareil 

 Reproducteur, 1854^ pi. x. fig. 4. 



8. Veetebrae of Constricting Serpent (Python Sp'^.). 



The vertebrae of Ophidia may be divided into three classes : the 

 first of which consists of the two anterior vertebrae corresponding 

 to the atlas and axis of anthropotomy ; the second of the trunk 

 vertebrae^ which in these animals possessed of no functional limbs 

 nor limb-girdles nor sternum^ all support moveable ribs, and corre- 

 sjDond with the posterior cervical, dorsal, lumbar, and sacral of other 

 Reptiles ; and the third of the caudal series which is placed pos- 

 teriorly to their anal outlet, and has the ribs anchylosed with the 

 other vertebral elements. The number of the first series is, probably, 

 constant in the Ophidia; that of the trunk vertebrae may vary 

 from one hundred to three hundred; that of the caudal is the 

 most variable, being in some snakes as few as five, and in others 

 as many as three hundred. The neural arches of all the vertebrae, 

 except the atlas, are anchylosed with their centra in the squamate 

 Reptiles, whereas in the loricate a neurocentral suture is permanent. 

 The Ophidia difier from all other Reptiles in having the anchylosed 

 costal elements of the anterior caudal vertebrae bifid on each side 

 for the protection of their lymphatic hearts ; and in the non- 

 development in the same region of detached chevron bones for 

 the protection of their caudal bloodvessels, for which however the 

 bifid exogenous hypapophyses form a channel at least in part of 

 their course. 



The special needs of these limbless animals are met by the ' ball 

 and socket ' articulation or ' enarthrosis ' of the procoelian bodies 

 of their vertebrae ; and by the presence of a 'zygosphene^ on the 

 anterior, and of a ' zygantrum ' on the posterior aspect of the 

 opisthocoelian roof of their neural canal, internally and superiorly 

 to the ordinary zygapophyses. The ' bair in the enarthroses of 

 the trunk and tail vertebrae of the Ophidia forms a larger portion 

 of a sphere, and that sphere a more perfect one than in ordinary 

 Reptiles. The socket for its reception is proportionately deeper, 



D 



