ANATOMY OE VERTEBRATES. 



47 



The Siren lacertina has between 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 



/is -m 





Skeleton of Lepidosiren anncctcns. xxxin. 



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 zygapophysis to the diapophysial part of the posterior 

 transverse process. Thence a third short ridge is continued to the 

 posterior zygapophysis. The vacuities between these several ridges 

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

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

 arid di-apophysial plates are developed from each side of the atlas, 

 which has also the posterior zygapophyses. In the second vertebra 

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



42 



30 



Skeleton of Tadpole of Itana csculenta 



transverse process, which supports a short straight pleurapophysis. 

 These elements are similarly developed from six or seven succes- 

 sive vertebrae. 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 haamal canal. In the Proteus, 

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

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



