ANATOMY OF VERTEBRATES. 



47 



The Siren lacertlna has betwe en eighty and ninety trunk-vertebrae. 

 They have many longitudinal ridges, the neural arch has coalesced 

 with the centrum, the neural spine forms the highest ridge and 

 bifurcates posteriorly to terminate upon the zygapophysis. A 



41 



skeleton of Lepidosircii anncctens. xxxiij. 



hypapophysial ridge forms, by defect of ossification on each side, 

 the under part of the centrum. A parapophysial ridge extends 

 from a short anterior parapophysis to the longer parapophysial 

 part of the posterior transverse process. A diapophysial ridge 

 extends above, and nearly parallel with the former, from the 

 anterior zygajiophysis to the diapophysial part of the posterior 

 transverse jn'ocess. Thence a third short ridge is continued ti3 the 

 posterior zygapoj^hysis. The vacuities between these several ridges 

 resemble those in the vertebra of some fishes. The body of the 

 atlas extends forward like a short odontoid process : short par- 

 and di- apoiihysial plates are developed from each side of the atlas, 

 which has also the posterior zygapoi^hyses. In the second vertebra 

 the par- and di-apophysial plates have united to form a compound 



42 



Skeleton of Tadiiole of liLuia csoilenta 



transverse process, which supports a short straight pjleurapophysis. 

 These elements are similarly developed from six or seven succes- 

 sive vertebrfe. In the tail the vertebra is compressed and vertically 

 extended by the bending down of the parapophysial plates to form 

 two vertical walls, intercepting a litemal canal. In the Proteus, 

 which has about sixty trunk-vertebra3, the third to the ninth in- 

 clusive support short ribs, attached to the lower (parapophysial) 



