204 ZOOTOMY, 



rudimentary first metacarpal is the single phalanx of the first 

 digit or pollex : the second digit has two phalanges, the 

 proximal one (ph.2) being flattened and very thin on its 

 post-axial side, the distal one (ph. 2') pointed and concave 

 dorsally: the third metacarpal bears a single pointed 

 phalanx (ph.$). 



10 1. In the young bird the metacarpals are distinct bones 

 with cartilaginous epiphyses. 



XIV. Make out the characters of the pelvis or hip 

 girdle as follows : 



102. It consists of two paired bones, the ossa inno- 

 minata (Fig. 50), more or less extensively ankylosed to 



il 



a.tr 



ac 



ol'f is 



FIG. 50. Columba livia. Left os innominatum of a nestling 

 (fourteen days), viewed from without ( x 2). 



The cartilage is distinguished by dotting. 



ac, acetabulum : a.tr, anti-trochanter : il, pre-, and zT, post- 

 acetabular portion of ilium : is, ischium : i.s.f, ilio-sciatic foramen : 

 ob.f, obturator fissure : ptt, pubis. 



the sacrum in the adult, but easily separable in the young 

 bird. 



103. The acetabulum (Fig. 48, ac), a rounded articular 

 cavity on the outer surface of each os innominatum, per- 

 forated by an aperture, and serving for the articulation of the 

 leg : its postero-dorsal region is prolonged into a distinct 

 facet, the anti-trochanter (a.tr). 



