8o rUOCEEDINGS OF THE 



Tlie Striiehire of tlie Vertebral Column in the Anura Phaneros^Iossa 

 and Its Importance as a Basis of CI issiticatiou. By Gko. E. 

 NiciiaLi.s, D.Sc!., F. [j.S., Bi;it Memorial Fellow, Department 

 of Zoology, King's College, Loudon. (With 1 Text-llgure.) 



[Read 1st June, 1916.] 



As is Well known, the vertebral column of the common frog 

 consists of nine vertebra? of which the ninth (the sacral) has a 

 biconvex centrum. Of the eight pre-sacral vertebrae, tlie first 

 seven are proccelous and the eigiith has a biconcave (amphiccelous) 

 c-jntrum. 



it is generally supposed that th's condition prevails among the 

 greater number of living Anur-i,aud this type of vertebral column 

 is commonly described (notwithstanding the condition of the eighth 

 and ninth vertebne) as proccelons, in distinction to that of those 

 few primitive Anura in which the presacral vertebrae are uniformly 

 02>i'<thontlous. 



Thus Gradow states ('oi, p. 19), "Procoelous A'ertebrae exist 

 in the overwhelming majority of the Anura: opisthocoelous are 

 those of the Aglossa, the Di^coglossidae, and of some PelobatidaB." 

 He continues (p. 20), " the sacral vertebra, . . . in all the Anura is 

 invariahhj biconvex, the eighth being biconcave in the procelous 

 families^' (iny italics). 



Now this generalization which had appeared, in almost identical 

 form, several years earlier in Boulenger's admirable work on "The 

 Tailless Batrachiaus of Europe," is, as I shall presently show, by 

 no means correct. 



The accuracy of the statement, however, appears never to have 

 been challenged, nor even the existence of exceptions recorded 

 until recently, when I called attention ('14, pp. 420-1) to the fact 

 that the condition of the eighth and ninth vertebra? of Bufo 

 constituted a veiy distinct departure from this rule. 



This fact had been ascertained by the examination of all of the 

 Bufonid skeletons in the Collection of the British Museum, this 

 material (with my own specimens) comprising more than fifty 

 examples i-epresenting over thirty species. In this genus the 

 centra of all of the vertebra? are alike excepting only that the con- 

 vexity (for articulation with the ensuing coccyx) upon the hinder 

 face of the ninth vertebra is doubled in the manner that is so 

 nearly universal among the Anura. 



In /?u/'o, then, there exists a third type of vertebral column 

 which is uniformhj proadous, and therefore perfectly distinct 

 from that which has a biconvex sacral and a biconcave eighth 

 vertebra but which, nevertheless, has hitherto been described as 

 prorffilous. It is obvious that only to such a vertebral column 

 as that of Bufo can the term " Procoelous " be strictly applicable, 

 in distinction to that of the lower Anura (Aglossa) in which the 

 vertebral column is o^^isthoadous. 



