1886.] 



DISK OF THE AXIS IN MAN. 



341 



modern anatomist doubted the existence of two lateral nuclei for the 

 main portion of the odontoid process ; but if any one examine the 

 axis of a human foetus at the eighth month of intra-uterine life, he will 

 have all doubts as to the duplicity of this centre removed (see fig. 2). 



Another matter of considerable interest is the existence or non- 

 existence of an epiphysial j)late for the upper surface of the true 

 centrum of the axis. Cunningham considers it to be absent ; but it 

 is certainly present, and may be detected in section of the axis at the 

 time the epiphysial plates make their appearance in other parts of 

 the spine. In Cunningham's paper reference is made to Macalister's 

 observation that the two epiphysial plates are present in the axis 

 vertebra of Batfenoptera rostrata, and that it can be detected in some 

 cases iu Man. Prof. Humphry has described and figured the upper 

 plate in a Rabbit. 



On the other hand, Prof. Flower' figures the axis of a man with 



Axis vertebra of a young Seal in section, showing the epiphysial plates 

 of the true centrum of the axis, e, e. 



these plates present, as though it were an accepted fact, but describes 

 the upper one as being represented by irregular ossifications. 



In order to test this point I have secured the axis vertebra from 

 many young animals. As a result of the investigation, I find two 

 epiphysial plates for the axis present in the following : — 



Primates. . . . Man. Spider-Monkey, Ateles paniscus ; Bonnet- 

 Monkey, Macacus sinicus. 



Ungulata . . Horse. Axis Deer. Giraffe. Sheep. 



Carnivora . . The Leopard. The Domestic Cat. Seal. 



Other anatomists have reported it in : — 

 Ungulata . . Foetal Horse (Macalister^). 

 Cetacea .... Balcenoptera rostrata (Macalister"). 

 Rodentia. . . . Rabbit (Humphry^), 



^ ' Osteology of tlie Mammalia.' 



° Journal of Anat. and Physiology, vol. iii. p. 54 ; and Phil. Trans. 1868. 



3 ' The Human Skeleton,' p. 129. " 



