392 THE ANATOMY OF VEETEBEATED ANIMALS. 



division into bracliiiim, antebracliium, and manus, but have 

 the form of a broad flattened paddle, without any vestiges 

 of nails. 



The one or two apertures by which the cavity of the 

 nose opens externally, are always situated at the top of the 

 head, and far removed from the extremity of the snout. 

 There is no third eyelid, and the very small auditory aper- 

 tures are totally devoid of any pinna. The teats are two, 

 and, in the female, are lodged in depressions on each side 

 of the vulva. 



The articular surfaces of the centra of the vertebrae are 

 flat, and the epiphyses usually remain distinct for a long time. 



The spinal column, as a whole, is remarkable for the 

 shortness of its cervical, and the length of its lumbar region, 

 there being sometimes a greater number of lumbar than of 

 dorsal vertebrae. There is no sacrum. The caudal vertebrae 

 are only distinguishable from the posterior lumbo-sacral 

 vertebrae by their chevi-on bones. The second vertebra of 

 the neck is devoid of any odontoid process ; and it very 

 commonly happens that more or fewer of the cervical 

 vertebrae, the bodies of which are often so short as to be 

 mere discs, are ankylosed together, either by their arches, 

 or by their centra, or by both. The centra of all the suc- 

 ceeding vertebrae are large in proportion to their arches, 

 and the inter-vertebral fibro-cartilages are exceedingly 

 thick, so as to confer great flexibility and elasticity on the 

 spine. The arches of the hinder dorsal vertebrae, and of 

 those of the lumbar and caudal regions, are not articulated 

 together by zygapophyses. The centra of the posterior 

 caudal vertebrae lose their processes and become polygonal. 



Yery few of the ribs become connected with the sternum 

 at their distal ends; and, in contradistiaction to what 

 happens in most Mammalia, the proximal ends of the 

 majority of the ribs are connected only with the transA^erse 

 processes of the vertebra, and not with their bodies. 



The skull is even more remarkably modified than the 

 vertebral column. The brain case itseK has a spheroidal 

 form; while the jaws are greatly prolonged, the principal 



