IV. VERTEBRATA: AVES. 



605 



S/- 



of life, under the influence of which all of the other organs exist. 

 The character of the skeleton, the respiratory organs, and in part 

 the sense organs and brain, are connected with the powers of flight. 



As the feathers of the wings, like the fins, form what may 

 be called a paddle working as a whole, the skeleton of these limbs is 

 simplified (fig. 634), first, by the reduction of the fingers, of which 

 only three with a small number of phalanges persist (j>,p',p")\ 

 second, by fusion of the corresponding metacarpals (m) with each 

 other and with the adjacent carpal 

 bones. On the other hand, in order 

 that there may be the necessary en- 

 ergy and the most complete transfer 

 of the same to the body, the con- 

 nexion with the skeletal axis is 

 strengthened by special development 

 of the parts. In the shoulder girdle 

 (fig. 635) all three elements are firm, 

 a sword-shaped scapula (s), a colum- 

 nar coracoid (c), and clavicles which 

 are usually united to a i wish-bone/ 

 or furcula (/). Clavicles and furcula 

 are united directly or by ligaments 

 to the broad sternum, the anterior 

 face of which is developed into a 

 strong keel, the carina, or crista 

 sterni, in order to give the largest 

 surface for attachment of the large 

 muscles of flight. Usually the greater 

 the powers of flight the more devel- 

 oped the carina, yet in some cases 

 (albatross) the weak carina is com- 

 pensated for by the enormous width 

 of the sternal plate. In running birds (ostriches, etc.) the 

 carina is entirely gone. The thoracic framework is rendered 

 more firm by the development of uncinate processes from the ver- 

 tebral parts of the ribs (u) which overlap the succeeding ribs. 



Since the fore limbs are no longer used for walking, the sup- 

 port of the body depends upon the hinder extremities, and this 

 has brought about two striking characteristics the broad union of 

 the pelvis with the vertebral column, and the simplification of the 

 leg skeleton. In the embryo the ilium (fig. 635, il) is connected 

 only with the two sacral vertebrae present in most reptiles, but 



Fm. 635. Trunk skeleton of stork. 

 (From Gegenbaur.) as, sternal 



rrt of rib ; c, coracoid ; era, keel ; 

 furcula (fused clavicles) ; /p, 

 fused spinous processes of thoracic 

 vertebrae; il, ilium; is, ischium; oc, 

 vertebral part of ribs; p, pubis; 8, 

 scapula; sp. spinous process; st,st', 

 sternum and abdominal processes; 

 ?t, uncinate processes; x, acetabu- 

 lum. 



