ELEMENTARY SKETCH OF THE OSTEOLOaY OF BIRDS. 29 



having the true pubis well developed, in place of being almost 

 or quite rudimentary. In those reptiles, on the other hand, 

 which habitually make use of both pairs of limbs in walking, 

 the post-pubis is never developed, while the true pubis is always 

 of large size. 



It would seem, therefore, that in birds and reptiles the de- 

 velopment of the post-pubis is correlated with the power of 

 walking on the hind-limb only, and that this development is 

 probably necessary for the proper balance of the body when in 

 this position. It also seems that when the fore-limbs cannot 

 be put on the ground at all, as in birds, that the true pubis 

 becomes practically rudimentary. 



For details respecting this very interesting and important 

 discovery, I must refer the reader to Professor Marsh's papers. 



R. L. 



