444 THE MECHANICAL FUNCTIONS. 



of the vertebrae. They may be regarded as 

 nidimental ribs.* 



The pelvis consists of two slender and elon- 

 gated iliac bones, which are extended backwards, 

 and which, at their anterior extremities, merely 

 touch the points of the transverse processes of the 

 last vertebra of the back. This vertebra is much 

 broader than the rest, and although it consists 

 but of a single vertebra, must be considered as a 

 sacrum. The two pubic and ischiatic bones are 

 exceedingly small, but still contribute to form the 

 acetabulum, or cavity for the reception of the 

 thigh bone, at the hinder extremity of the slender 

 bones above mentioned. This is the simplest 

 possible form to which the pelvis can be reduced, 

 while it preserves its attachments to the spine. 

 It presents in this respect a more advanced stage 

 of developement than that of fishes. 



The connexion of the bones of the anterior 

 extremities witli the spine is analogous to that 

 which takes place in rays and sharks : there 

 being an osseous belt formed by the scapula, 

 clavicle, and coracoid bone, with the latter of 

 which the humerus is connected. The sternum 



* The plan of reproduction in these animals requires that the 

 ovary, or organ which contains the eggs, should be capable of 

 enormous dilatation, in order to contain the immense bulk to 

 which these eggs are expanded, previous to their being brought 

 forth. It was probably in order to make room for this dilated 

 ovary that the ribs have not been developed. 



