70 PROF. G. B. HOWES AND MR. H. H. SW1NNERTON ON THE 



applying to the former condition the term Arc/ticraniate 1 , and to the latter that of the 

 Syncraniate. 



The characters of the occipital condyle and the presence of one, two, or, for the 

 matter of that, of three conclyles, no longer have the significance once attached to them 

 as criteria of affinity. 



Judged from this point of view, the Rhynchocephalia may well be regarded as a 

 lowly group, ancestral to the Sauropsida as ordinarily defined, and intimately related 

 to the Anomodontia ; and while the latter, perhaps with or through the Pelycosauria of 

 Cope, on the one hand gave rise to the Mammalia, they were probably with the Rhyn- 

 chocephalia derived by diversity of modification from some common ancestral stock 

 which carries us towards a group which must have been either Batrachian Reptiles or 

 Reptilian Batrachians, as compared with forms extant i. e. 9 they either possessed a 

 coraco-sternum and an archicranium, or a costal-sternum and a syncranium, structural 

 combinations which go hand in hand. If they were of the latter type, the living 

 Batrachia must have suffered the loss of a costal-sternum and not a few of their 

 distinctive characters must be indicative of retrogression. The argument applies 

 equally to the quadrate and whether its representative in the living Batrachia is or is 

 not vestigial, and, as concerning the parasphenoid and pterygoids, the question arises 

 whether in these ancestral forms they did or did not reach the vomers. 



On the other hand, it is possible that, in some manner yet to be discovered, the 

 ancestral series of Terrestrial Vertebrata may have combined the characters of the later 

 differentiated forms, as Gadow has surmised in his sagacious remark 2 that " the 

 Amphibia and Reptiles do not form a continuous line of development, but are two 

 divergent branches of a common stock of Palaeozoic Tetrapoda." If, with Credner, we 

 group together the Stegocephalia and " Proganosauria " as the " Eotetrapoda" 3 , or with 

 Dawson and Baur 4 associate a no less heterogeneous assemblage under the cognomen 

 " Microsauria," we but imply the conviction herein set forth. 



Concerning the phalangeal problem, the discovery that certain living Chelonia are 

 hyperphalangeata 5 ; that by Peters 6 ' that in the Pleurodian Pelomedusa the numerical 

 reduction of the phalanges is in part due to fusion of more numerous elements during 



1 Sewertzoff writes (Bull. Soc. Nat. Mosc. u. s. vol. ix. 1895, p. 180) : "Bei die Amphibien entspricht tier 

 Ganze Occipibalabschnitt einem ein/igen Segmente, dein einfachen Occipitalbogen, so dass die Amphibien in 

 dieser Hmsicht unter alien Cranioten, mit Ausnahmc der Petromyzonten, die einfachsten Zustand zeigen." 

 Intensely interesting in this association are the recent observations of Peter (op. cit. [antea, p. 50] pp. 590- 

 592), based on the discovery in Ichthyophis of a postvagal nerve, having, it would seem, an essential similarity 

 to the " spinal accessory " of the Amniota. 



a Gadow, H. : Phil. Trans, vol. 187. 1896, p. 23. 



3 Credner, H.: Allgem. Verstell. naturwiss. Abhandlg. Berlin, Hft. xv. 1891 (" Naturwiss. Wochenschr."), 

 pp. 1-52. 



1 (?/. Baur, G. : Anat. Anz. Bd. xiv. 1897, p. 148, and Bd. xi. 1896, p. 657. 



8 Of. Boulenger, G. A. : Brit. Mus. Cat. Chelonians, 1889, p. 240, espec. Chitra. 



B Peters, W. : Reise nach Mossambique, Zool. iii. Berlin, 1882, p. 6. 



