144 



VERTEBRATA: AVES OR BIRDS. 



TIG. 163. 



I 



. 3 



w 



1 



o. 



SkuU of a Bird Eagle. 



ossified throughout their whole length, in order to give 

 greater strength to the trunk ; and a small bone is at- 

 tached obliquely across each rib, which also contributes to 

 the same result. 



Regarding the wrist as part of the hand, each wing is 

 made up of three sections, the arm, forearm, and hand, 

 thus corresponding to the anterior extremities of man 

 and other mammals. 



The hind locomotive members of Birds are each com- 

 posed of a femur, a tibia and fibula, the last two more or 

 less united ; a tarsus and metatarsus, the latter more or 

 less merged in the former ; and generally of three toes 

 before and a thumb behind, the latter, however, some- 

 times wanting. 



