342 THE INTERVERTEBRAL DISK OF THE AXIS IN MAN. [June 29, 



As the upper epiphysis of the axis exists in forms so widely dif- 

 ferent as a Cat and a Whale, or a Monkey and a Horse, there can be 

 very little doubt that it is a very general condition which has been 

 overlooked simply because it has not been sought. 



The reason why I have been able to give an account of the axis in 

 the specimens enumerated in the preceding list is explained by the 

 fact that for some time past I have been collecting immature axes 

 for another purpose; thus, having a goodly stock, I utilized them 

 for the purpose of this paper. 



As a matter of convenience the following list of probable dates in 

 the appearance of the individual nuclei of the axis is appended : — 



Centres for laminae, 8th week. 

 Centres for body, 12th to 16th week. 

 Nuclei for os odontoideum, 5th month. 

 Centre for tip of odontoid process, 2nd year. 

 Epiphysial plates, about 16th year. 



By the twentieth year all parts of the bone are consolidated, 

 except the lenticular portion between the axis and the odontoid 

 process. 



The interest of the question centres itself around the additional 

 evidence aflForded to the view that the odontoid process is the body 

 of the atlas united with the axis, as was hinted by Cuvier, but first 

 clearly made out by the admirable researches of Rathke', and 

 subsequently confirmed by many competent observers. 



P.S. (July 30th, 18n6). — In the discussion which followed the 

 reading of this paper, Mr. J. W. Hulke drew attention to the im- 

 portance of the above observations in so far as they independently 

 confirmed Prof. Albrecht's recent view expressed in a paper entitled, 

 " IJber die Wirbelkorperepiphysen und Wirbelkorpergelenke zwischen 

 dem Epistropheus, Atlas und Occipitale der Saugethiere." (See 

 ' Die Comptes Rend us der achten Sitzung des internationalen medi- 

 cinischen Kongresses, Kopenhagen,' 1884.) 



At the time my paper was read I was ignorant of Albrecht's re- 

 search in this particular direction. However, a careful perusal of 

 the paper in question convinces me that the epiphysis in the midst 

 of the axis really represents, as Albrecht insists, two epiphyses, viz., 

 that belonging to the cranial end of the axis and that appertaining 

 to the caudal end of the atlas (odontoid process). Regarding the 

 "centroidal" masses more observations are required, and the subject 

 is one of great interest. 



' 'Entwickelung der Schildkroten.' 



