Zoological Society* 431 



has given, or the skeleton itself, with the cervical vertebrae of almost 

 any other mammiferous quadruped, it is most easy to perceive that 

 the eighth and ninth vertebra? of the Sloth differ from the other cer- 

 vical vertebrae in precisely the same manner as do the sixth and 

 seventh vertebrae of other Mammalia from those preceding them in 

 the series. He observes, in describing the eighth vertebra, " In the 

 first dorsal each transverse is completely divided into an anterior 

 flattened process, which is turned forwards, and a true lateral or 

 transverse one, which supports the little articulated rib. The trans- 

 verse process is smaller, but considerably longer, than those of the 

 true cervical, and stands more in a lateral or transverse direction." 

 These characters are precisely the same, excepting that the little 

 articulated rib is wanting, in the sixth vertebra of nearly all Mam- 

 malia, and in most of them still more distinctly and strikingly ma- 

 nifested. But in the excellent description given by the learned 

 professor, one point at least has been omitted, and that is the exist- 

 ence of the foramen for the vertebral artery in the eighth vertebra of 

 the Sloth : no doubt the coexistence of the same foramen in the upper 

 vertebrae will account for its not being mentioned, but its presence 

 tells strongly in favour of the cervical nature of the vertebra. 



The transverse process of the seventh cervical of the Sloth, also so 

 carefully described by Professor Bell, accords exactly with that of the 

 fifth of other Mammalia, in presenting a character intermediate 

 between that which precedes and that which follows it. In speaking 

 of the ninth vertebra of the Sloth, he proceeds, " In the second dorsal 

 vertebra the anterior processes do not exist, and the body assumes 

 the form of the succeeding ones. The transverse processes are 

 simple and obtuse, and the articular surface is slightly excavated." 

 I have already pointed out the character presented by the seventh 

 cervical in most Mammalia, which will be seen to agree well with 

 that just cited of the ninth in the Sloth. 



In the skeleton examined by myself, the upper pair of rudimental 

 ribs, that is, those attached to the eighth vertebra, are wanting — no 

 doubt accidentally lost, and therefore in no way influencing the pre- 

 sent argument ; but the second pair, attached to the ninth vertebra 

 in a manner just similar to that which I have noticed as occurring 

 abnormally in the Polecat, have contracted a complete anchylosis 

 with the extremities of the transverse processes to which they are 

 connected, thus showing, what it seems that Professor Bell's speci- 

 men did not exhibit, that this rib is not permanently moveable, but 

 at some period of life becomes a fixture. The figure given by Pro- 

 fessor Bell in illustration of his most valuable paper does not show 

 any indication of the existence in the transverse process of the ninth 

 vertebra of the foramen for the passage of the vertebral artery ; but 

 as this foramen is but small, and the position in which the figure is 

 taken not a very favourable one for exhibiting it, it may nevertheless 

 have existed in his specimen ; the minute foramen which he mentions, 

 " for the passage of intercostal vessels," must be one pierced in the 

 rib itself. In the specimen which I examined however, we have the 

 ninth vertebra presenting the foramen for the vertebral artery, en- 



