IV. VERTEBRATA: AVES 



53£ 



spending 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 borly, the con- 

 nexion with the skeletal axis is strengthened by special development of the 

 parts. In the shoulder girdle (fig. 586) all three elements are firm, a 

 sword-shaped scapula (s), a columnar coracoid (<"), and clavicles which 

 are usually united to a 'wish-ljone,' or 

 Jitrcula (/). 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, in order to give the largest sur- 

 face for attachment of the large muscles 

 of night. Usually the greater the powers 

 of flight the more developed the carina, 

 yet in some cases (albatross) the weak 

 carina is compensated for by the enor- 

 mous width of the sternal plate. In 

 running birds (ostriches, etc.) the carina 

 is entirely gone. The thoracic frame- 

 work is rendered more firm Ijy the de- 

 velopment of uncinate processes from the 

 vertebral parts of the ribs {u) which 

 overlap the succeeding ribs. 



Since the fore limbs are no longer 

 used for walking, the support of the body 

 depends upon the hinder extremities, 

 only the toes reaching the ground, the 

 middle foot {ineta podium) increasing the 

 length of the leg. 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. 586, it) is connected only with the two sacral 

 vertebra; present in most reptiles, but later it extends forward and back, 

 uniting with from nine to twenty-three vertebra; ; while the iliac bones 

 of the two sides may meet dorsal to the vertebral column. This ex- 

 tensive union of pelvis and axial skeleton is understood when we recall that 

 the vertebral column is not vertical as in man, but is inchned. Ischium 

 and pubis are peculiar in that they extend backwards, parallel to each 

 other, from the acetabulum, and that only exceptionally (ostrich) are the 

 bones of the two sides united by a symphysis. 



Fig. 586. — Trunk skeleton of 

 stork (from Gegenbaur). as, sternal 

 part of rib; c, coracoid; crs, keel;/, 

 furcula (fused clavicles); fp, fused 

 spinous processes of thoracic verte- 

 bra:; il, ilium; is, ischium; oc, verte- 

 bral part of ribs ; p, pubis ; s, scapula ; 

 5^, spinous process; st, sl\ sternum 

 and aljdominal processes; 2t, unci- 

 nate processes; x, acetabulum. 



