334 BAUR. [Vol. IV. 



Of course the direct proof of splitting of myotomes could only 

 be given by the study of the living embryo, which, if possible 

 at all, is exceedingly difficult. If we have the complete seg- 

 ments in the embryo or in the adult animal, we cannot decide 

 whether they consisted originally of a single myotome, or 

 whether they are the result of division. For instance, in the 

 peculiar consolidation of vertebrae in snakes, mentioned by 

 Owen, and also observed by me at different times, we do not 

 know whether this consolidation is the result of real union 

 of two segments, or of partial division of one segment. At 

 least we may adopt one explanation just as well as the other. 

 I am inclined, however, to accept partial division in these 

 cases. A great number of observations is necessary to see 

 in what relations the frequency of such consolidation stands 

 to the increased number of segments ; in other words, whether 

 such complexes are more frequent in animals with the number 

 of segments considerably increased, as it appears to-day, than 

 in such which have a relatively small number. 



By very careful study and comparison of the structure of the 

 single vertebrae, however, it is sometimes possible to determine 

 whether we have a case of intercalation or not. It is well known 

 that the typical number of the presacral vertebrae in the living 

 Crocodilia is twenty-four ; there are two sacrals : the first caudal 

 is peculiar, by being biconvex. In a specimen of Gavialis 

 gatigeticiis I found twenty-five presacral vertebrae. ^ As in all 

 living Crocodiles the first caudal vertebra is biconvex ; but in 

 this case it is the twenty-eighth, in the other the twenty- 

 seventh. Is it not evident, therefore, that at some place be- 

 tween the occipital condyle and the first caudal a new vertebra 

 has beeen inserted .^ By careful comparison I find that this 

 new vertebra has been intercalated between the ninth and 

 tenth. 



A similar case I have observed in Heloderma. In this 

 lizard the first caudal vertebra has also a peculiar character. 

 The small rib connected with it is perforated ; this perforation 

 is absent in the other vertebrae. By this peculiarity the first 

 caudal vetebra is distinguished from the rest. Four specimens 

 of Heloderma show the following condition. In the first speci- 



^ G. Baur : Anzahl der praesacralen Wirbel der Crocodilia. Zool. Anz. No. 238, 

 1886. 



