340 MR. J. B. SUTTON ON THE INTERVERTEBRAL [JunC 29, 



body and two additional centres for the epiphysial plates, as in other 

 regions of the spine. When the segments of the sacrum commence 

 to ankylose, the adjacent epiphysial plates fuse with each other 

 before they join the bodies of the vertebrae to which they belong. 

 This fusion of epiphyses is of a deceptive character, for it does not 

 occur throughout the whole width of these bony menisci, but only 

 around their circumferences. Hence if a section be carried through 

 the sacrum, a piece of cartilage may be detected situated in a central 

 cavity, the boundaries of which are constituted by the epiphysial 

 plates ; this piece of cartilage persists long after the various seg- 

 ments of the sacrum have, from all external evidence, become 



Fig. 3. 



A section through the human sacrum, showing the epiphysial plates uniting 

 with each other peripherally before fusing with their centra. 



firmly united. This remarkable arrangement of the epiphysial plates 

 is represented in fig. 3. 



It is quite possible that this mode of fusion is applicable to the 

 cervical vertebrae of Whales ; for an examination of this region of the 

 column in a young Porpoise shows well-marked indications of 

 peripheral union of the epiphysial plates, whilst they are still 

 separate from the bodies of the vertebrae to which they respectively 

 belong. My attention was first drawn to this question when 

 examining the sacral vertebrae of a young skeleton of the Great 

 Anteater, Myrmecophaga jubata. After the skeleton had been 

 macerated, the sacrum broke up into its component elements, the 

 epiphysial plates separated from the vertebrae, but the contiguous 

 plates were firmly united in pairs. 



So far as my observations on other mammals have extended, this 

 mode of fusion appears to be general. 



There are other points in the axis which demand some notice. I 

 was unaware, until reading Prof. Cunningham's j)aper, that any 



