THE PIGEON. 205 



104. The ilio-sciatic foramen {t.s.f), a large aperture 

 immediately posterior to the acetabulum. 



105. The pubis {pu), a slender' bony rod, forming the 

 ventral part of the acetabulum and the ventral border of 

 the post-acetabular portion of the innominate bone : it is 

 separated from the rest of the bone by a long cleft, the 

 obturator fissure {ob.f). 



106. The ischium (is), consisting of that part of the 

 post-acetabular portion of the innominate bone which lies 

 above the obturator fissure and below and behind the iho- 

 sciatic foramen : at the acetabulum it is ankylosed with the 

 anterior end of the pubis. 



107. The rest of the os innominatum is formed by the 

 ilium (//, //'), which consists of pre- and post-acetabular 

 portions, the former (il) ankylosed at the ventral boundary 

 of the acetabulum with the pubis, the latter (2'/') ankylosed 

 with the ischium in the postero-dorsal region of the 

 acetabulum, as well as behind the ilio-sciatic foramen. 



108. In the young bird the os innominatum consists of 

 a distinct mass of cartilage of the same shape as the adult 

 bone, in which the ilium, ischium, and pubis are formed, 

 as separate ossifications, which unite with one another at a 

 later period. 



XV. In the leg make out : 



109. Its general composition ; it consists of a proximal 

 division, containing a single bone, the femur ; a middle 

 division, the crus or shank, containing a large bone, the 

 tibio-tarsus, and a small and imperfect one, the fibula ; 

 and a distal division, the pes, formed of a cylindrical 

 bone, the tarso-metatarsus, to which four digits are 

 attached. 



no. The position of the parts: the femur is directed 

 downwards and forwards from its articulation with the 



