470 MANUAL OF ZOOLOGY sect. 



ends ; the proximal end is produced pre-axially, into an 

 outstanding step-like process. 



The study of its development shows that this bone is 

 formed by the union of the distal carpals with three meta- 

 carpals (Fig. 282), the second and third of which are the 

 two rod-like portions of the bone, the first, the step-like 

 projection. Articulating with the first metacarpal is a single 

 pointed phalanx (ph. 1) ; the second metacarpal bears two 

 phalanges, the proximal one (ph. 2') produced postaxially 

 into a flange, the distal one (ph. 2") pointed ; the third 

 metacarpal bears a single pointed phalanx (ph. J). 



Fig. 283. — Columba livia. Left innominate of a nestling. The cartilage is dntted. 

 ac, acetabulum; a. tr, anti-trochanter; il, pre-acetabnlar ; and //', post-acetab- 

 ular portion of ilium; is, ischium; i s.f, ischiatic foramen; oh./, obturator 

 notch; pit, pubis. (From Parker's Zootomy.') 



The pelvic girdle (Fig. 283). The ilium (il) is an 

 immense bone, attached by fibrous union with the whole 

 of the syn-sacrum and becoming ankylosed with it in the 

 adult. As usual it furnishes the dorsal portion of the acetab- 

 ulum. The ventral portion of the acetabulum is furnished 

 in about equal proportions by the pubis and ischium 

 (Fig. 283) : it is not completely closed by bone, but is 

 perforated by an aperture covered by membrane in the 

 recent state. Both pubis and ischium are directed sharply 



