| OCR Text |
Show 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 nonexistence of an epiphysial plate 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 Balaenoptera rostrata, and that it can be detected in some cases in Man. Prof. Humphry has described and figured the upper plate in a Rabbit. On the other hand, Prof. Flower1 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, 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 (Macalister2). Cetacea .... Balaenoptera rostrata (Macalister2). Rodentia Rabbit (Humphry3). 1 'Osteology of the Mammalia.' 2 Journal of Anat. and Physiology, vol. iii. p. 54; and Phil. Trans. 1868. 3 ' The H u m a n Skeleton,' p. 129. |
