204 



The two most remarkable cases of this series are doubtless tiic 

 two specirriiiia mentioned first, as to my knowledge they have not 

 yet been described. One of them is represented in F'ig. J. 



Fig. 1. 



Alius with bilateral ponticulus lateralis and bilateral 



ponliculus posterior. 



Rises the question about the morphological signification of these 

 variations. 



Among the investigators that have tried to give an answer to this 

 question, there are especially three, who claim the attention here, 

 viz. Lk Double, Bolk and dk Buklet. 



Le Double explains the occurrence of the above-described ponticuli 

 posteriores simply mechanically and regards it as ossification of a 

 ligament, which in most cases is found between the upper-posterior-rim 

 of the massae laterales and the upper- rim of the most latei-al part 

 of the arcus posterior atlantis. This ossification would take place 

 under the influence of the pulsations of the arteria vertebralis. 



In consequence of the curving of this artery at this place the 

 convexity of which is directed backwards, every pulse-gulf would 

 push the above-described ligament backward ; thereby a traction 

 would be occasioned on the periost of the atlas on the spot where 

 the ligament is fastened and under the influence of the stimulus the 

 osteogenetic potency of the periost would be increased. Le Double 

 cites, as an explanation of the occurrence of the ponticuli laterales, 

 an ossification of a ligament occasioned by the same causes. 



It seems to me very improbable that the cause of the formation 

 of the mentioned variations is to be found in the pulsations of the 

 A. vertebralis. In the first place it is very improbable that a so 

 typical variation should exclusively be dependent upon outward 

 circumstances, the more so, as these circumstances are pretty well 

 constantly' existing, and the frequency of the variation, though not 

 unimportant, is after all not so great as might be expected in 



kolom bij den menscli en hunne beteekenis. Nederl. Tijdsclir. v. Geneesk. 1899 

 Dl. 1, 11, 190.). Dl. 1. 



L. Bulk. Zur Frage der Assimilation des Atlas am Schadel beim Menschen. 

 Anal. Anzeiger Bd. XXVlll. 



