AXIAL SKELETON OF THE OSTRICH. 437 



The Pubis. 



The pubis is an exceedingly long and narrow bone, extending postaxiad and ventrad 

 from the acetabulum to considerably beyond the postaxial extremity of the ilium, yet 

 not so much so relatively in the young as in the adult. 



The pubis first curves slightly downwards, as well as strongly postaxiad, then some- 

 what dorsally and outwards, then inwards and venti'ad, and curves sharply round 

 directly ventrad, and afterwards and finally preaxiad, at the same time meeting its 

 fellow of the opposite side in a postaxial and ventral pubic sympyhsis. 



In the adult the pubis anchyloses with the ischium (fig. 71, i). 



The pubis forms a small ventral portion of the margin of the acetabulum (fig. 74,2^). 



LATERAL ASPECT OF THE ACETABULAR REGION OF AN IMMATURE PELVIS 



(J natural size). 

 Fig. 74. 



I' 

 a, acetabulum ; il, ilium ; is, ischium ; p, pubis. 



It develops a ridge on its dorsal aspect a little behind the acetabulum, which ridge 

 makes a projection dorsad in the ventral margin of the obturator foramen. 



The pubis does not seem to take any share in forming the ilio-pectineal spine. 



At its ventral convexity the ventral margin of the pubis may, at about its middle, 

 develop a bony process. This process is generally, however, only represented by a 

 slight thickening of the margin. To this point a small distinct bone' is sometimes 

 attached, which, when it becomes anchylosed, constitutes the process referred to as 

 occasionally present. 



The Ischium. 



The ischium is the shortest of the three pelvic bones. Narrow for the greater part 

 of its length, it expands at each end. 



Preaxially it anchyloses with the ilium dorsally, and with the pubis ventrally. 



Postaxially it anchyloses with the pubis (fig. 71, i), but not at all with the ilium. 



It forms about a third (the postaxial ventral third) of the margin of the acetabulum, 

 and the ventral half of the antitrochanteric process (fig. 74, is). 



From the outer postaxial margin of this process a sharp ridge continues ventrad upon 



' This bone has been described and figured by Mr. A. H. Garrod (in the Proc. Zool. Soc. for March 1872, 

 p. 359), who has suggested the possibility of its representing the marsupial bone. 



