274 



SEITARO GOTO. 



ninth vertebra. The anterior surface of the centrum presents a somewhat 

 kidney-shaped concavity to articulate with the similarly shaped convexity 

 of the ninth vertebra ; the centrum is grooved along the mesial line on the 



ventral surface, and its posterior end pres- 

 ents two convex articular facets, which are 

 slightly asymmetrical. The dividing line 

 between the two facets are not so deeply 

 cut as in the normal sacrum. 



In the cases 3, 4, and 5 above describ- 

 ed, we have a backward homceosis of the 

 sacrum. The intercalation theory of Baur 

 L'91] and others has not found favor with 

 later observers [Parker, '96 ; Adolphi, '96 ; 

 Bumpus, '97 ; Waite, '97 ; Ridewood, '97], 

 and there is no doubt that such cases as 

 those described in this paper can be ex- 

 plained more naturally and with less 

 difficulty by the theory of homceosis, 

 especially as there is abundant evidence that an extra free vertebra can be 

 added from the urostyle. 



With regard to the position of the sacrum in the Anura, the following 

 quotation from Gadow's recent text-book may be in place, as giving a 

 general aperçu of the subject [Gadow, : 01, p. 22 ct seq.~\ 



" The sacrum is formed by the ninth vertebra, but there are a few 

 interesting exceptions. Pelobates, Pipa, and Hymenochirus possess two 

 sacral vertebrae ; and neglecting individual abnormalities, these three 

 genera form the only exception among recent Amphibia. In the three 

 genera the coccyx is fused with the second sacral vertebra, and such a 

 fusion occurs elsewhere normally only in Bombinator with its single sacral 

 vertebra. The morphologically oldest condition is normally represented 

 by Pelobates, the sacral vertebra being the tenth and ninth. One case has 

 been recorded by Boulenger of Bombinator pachypus with eleven 

 segments, the last carrying the ilium. Individual lop sided abnormalities 



Cut 5. 



