1891.] HEI-ODERMA HORRIDUM AND H. SUSPECTUM. 113 



of these five parts had co-ossified." I can, however, now confidently 

 affirm that Dr. Shufeldt has been deceived in his examination. The 

 atlas-ring of Heloderma is formed, as in all Reptiles, of three pieces, 

 a ventral and two dorso-lateral. The presence of five elements in 

 the atlas-ring, if such had been the case, would have entirely upset 

 the current view on the morphology of the vertebral column, which 

 holds the said ring to be formed of the neural arch of the atlas and 

 the proatlanto-atlantic hypapophysis or intercentrum ; the centrum 

 of the atlas being either free behind the ring or fused with the 

 centrum of the vertebra following (odontoid process of the epistro- 

 pheus). I regard the views held by Cojie', Baur", and Credner' 

 on the morphology of the vertebral column, based as they are on the 

 evidence of the primitive structure afforded by many Stegocephalians, 

 as thoroughly sound, and borne out l)y everything we know of the 

 structure of recent and fossil Reptiles. 



The vertebrae of Reptiles are composed of the following 

 elements : — Neural arch (neurapophyses), centrum, and inter- 

 centrum (hypapophyses, subvertebral wedge-bones, chevrons). No 

 Reptile shows an exogenous hypapophysis together with an auto- 

 genous hypapophysis, wedge-bone or chevron on the same centrum ", 

 and the continuity of the series of intercentral autogenous hypapo- 

 physes throughout the vertebral -column, together with the gradual 

 passage of the wedge-bones into the chevrons, is clearly exhibited in 

 Sphenodon and the Geckos. The homology of the cervical hypapo- 

 physes with the chevrons is further manifested by such Squamata 

 as have the chevrons attached to a single centrum, viz., the Anguidce, 

 Varanidte, and Mosasauridce, having the cervical hypapophyses like- 

 wise on the centrum ; whilst those having the chevrons intercentral, 

 viz., ih&AgamidcB, Iguanidce, Lacertidce, most Scincidce, Chamceleon- 

 tidcE, &c., have also the cervical hypapophyses so disposed. 



In Sphenodon and Geckos, in which the branches of the anterior 

 chevrons are united at the base, the hypapophysis anterior to the 

 first chevron is single, but when the chevrons are V-shaped the 

 hypapophysis preceding them is paired. Such is the case in Helo- 

 derma, and I have observed the same thing in many other Lizards, 

 where these little bones bear much resemblance to the cervical hypa- 

 pophyses of many Chelonians, or of Lacerta agilis, as figured by 

 Leydig (Deutschl. Saur. pi. iv. fig. 53). I believe, however, that 

 paired autogenous hypapophyses have not been recorded before in 

 the caudal region of Lizards. The paired inferior processes of the 

 caudal vertebrae of Snakes must be likewise regarded as homologous 



1 Amer. Nat. 1878, p. 327, and Tr. Am. Philos. Soc. (2) xvi. 1888, p. 243. 



2 Biol. Centralbl. vi. 1886, p. 332. 



3 Zeitscbr. cleutsch. geol. Ges. xlii. 1890, p. 260. 



* HuLke (P. Z. S. 1888, p. 422) states that in the cervical vertebrae of Tra- 

 ckydosaurus rugosus " the ' intercalary ' or intercentrum coexists with a genuine 

 [exogenous] hypapophysis ;" but I have been unable to find any substantiation 

 of this statement on a specimen of that Lizard in the College of Surgeons, 

 which I have had especially cleaned for examining this point. It is possible 

 that the part termed by Hulke intercentrum is an epiphysis of the hypapophysis 

 such as is so well developed in Varanus and Mosasauria. 



Proc. Zool. Soc— 1891, No. VIII. 8 



