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Show 114 MR. G. A. BOULENGER ON THE OSTEOLOGY OF [Jan. 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)1 or not (Liodon), passing into true chevrons. As to the term to be employed for the element under discussion, we have the choice between Owen's hypapophysis 2 and Cope's later intercentrum. The objection that m a y 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 be3 and fused with the centrum. And Cope's term 1 The chevrons are also anchylosed to the centrum in Diploglossus and Ophi-saurus. 2 The term hcemapophysis should be entirely discarded, as based on a theoretical 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 "hcemal spine" stands for the cervical hypapophysis of Iguana, the hypapophysial epiphysis of the cervical vertebra? of Clidastes, as well as for the chevrons. The denomination hcemal 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 Rabbit. 3 O n 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 nigropunctatus; nat. size. ber of the family Teiidce, I find a very curious form of chevrons: the branches are in their proximal portion horizontal and applied against the centrum posterior to their intercentral attachment, the descending portion originating a little in advance of the middle of the centrum. W e may easily imagine that such an arrangement may lead, by the fusion of the basal portion of the hypapo-pnyses with the centrum, to a form of chevron comparable to that of a Varanus, Dut by a totally different process of evolution. By the way, it m a y be men- |