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 feetus 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 plate for the upper surface of the ¢rue 
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 Balenoptera rostrata, and that it can be detected in some 
eases in 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 
Fig. 4. 
Axis vertebra of a young Seal in section, showing the epiphysial plates 
of the true centrum of the axis, ¢, ¢. 
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 pot I have secured the axis vertebra from 
many young animals. Asa result of the investigation, I find two 
epiphysial plates for the axis present in the following :— 
Primates.... Man. Spider-Monkey, Aéeles 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 .... Balenoptera rostrata ( Macalister’). 
Rodentia.... Rabbit (Humphry °*). 
1 © Osteology of the Mammalia.’ 
2 Journal of Anat. and Physiology, vol. iii, p. 54; and Phil. Trans. 1868. 
3 «The Human Skeleton,’ p. 129. 
