114 MR. G. A. BOULENGER ON THE OSTEOLOGY OF [Jail. 20, 



with the chevrons, especially if we look at the state of things in the 

 anterior caudal region in the Mosasaurs, where we find distally 

 disconnected paired hypapophyses, whether fused with the centrum 

 (Mosasaurus) ^ or not (^Liodon), passing into true chevrons. 



As to the term to he employed for the element under discussion, 

 we have the choice between Owen's liypapophysis ^ and Cope's later 

 intercentrum. The objection that may be made to the former term, 

 of implying a process of the centrum, may be set aside from the 

 fact that Owen himself intended it for auto- as well as exogenous 

 formations, the two being, as far as Reptiles are concerned, certainly 

 homologous — the exogenous hypapophyses of the cervical region of 

 certain Lizards and Snakes, and of the caudal region of Snakes and 

 certain Mosasaurians, being nothing but the primitively autogenous 

 and intercentral elements (intercentra) shifted forwards or backwards 

 as the case may be ^ and fused with the centrum. And Cope's term 



^ The chevrons are also auchylosed to the centrum in Diploglossus and Ophi- 

 sawnis. 



^ The term hcBmapophysis should be entirely discarded, as based on a theo- 

 retical conception which is not borne out by our present knowledge. The loose 

 application of the term hcemal spine by Owen is best shown in one of his later 

 papers (Quart. Journ. Geol. Soc. 1877, p. 709), where " hcsmal spine" stands 

 for the cervical hypapophysis of Iguana, the hypapophysial epiphysis of the 

 cervical vertebrje of Clidastes, as well as for the chevrons. The denomination 

 hmmal crest or hcemal spine should be restricted to such ventral outgrowths of 

 the centra as the keel found in many Chelonians or the long process of the 

 lumbar vertebrae of the Eabbit. 



^ On examining a large variety of skeletons of Lizards, it is obvious that the 

 intercentral chevrons have in most cases been shifted forwards, as every passage 

 can be found between the position they occupy in Gecko and Iguana on the one 

 hand, and Varanus and Mosasaurus on the other. But in Tupinambis, a mem- 

 Fig. 4. 



Caudal vertebra of Tupinambis tiigropunctatus ; nat. size. 



ber of thefamily Teiidm, I find a very curious form of chevrons : the branches 

 are in their proximal portion horizontal and applied against the centrum pos- 

 terior to their intercentral attachment, the descending portion originating a 

 little in advance of the middle of the centrum. We may easily imagine that such 

 an arrangement may lead, by the fusion of the basal portion of the hypapo- 

 physes with the centrum, to a form of chevron comparable to that of a Varanus, 

 but by a totally different process of evolution. By the way, it may be men- 



