AXIAL SKELETON OP THE OSTRICH. 435 



The greatest transverse diameter of the entire pelvis is across the pubes, at about 

 the middle of thek antero-posterior extent. 



The greatest transverse diameter of the ilio-sacral mass is between the antitro- 

 chanteric processes. 



The pelvis when viewed ventrally (fig. 7 3) presents, of course, relations corresponding 

 with those akeady noticed as shoivn by the dorsal view. Here, however, the two ilio- 

 pectineal eminences (//;) are very conspicuous, diverging, as they do, preaxiad from the 

 preaxial end of each pubis. 



The rough surface for the attachment of a small bone, or else a bony process, is also 

 noticeable at about the middle (pre- and postaxially) of the ventral surface of each 

 pubis. 



The ventral surface of the sacrum is \'isible throughout, forming one elongated bone 

 in the middle line (in the adult), except that sometimes the last (twenty-second) sacral 

 vertebra shows the line of junction of its centrum with that of the twenty-first sacral 

 vertebra. 



This median bone, then (formed of the coalesced centra), is widest in front of the 

 acetabula, where it is concave transversely, and finally (between the two postaxial 

 halves of the postacetabular parts of the ilia) it is flat, with successive pairs of antero- 

 posteriorly directed excavations with a bony median ridge between each such pair of 

 excavations. 



The sacrum tapers backwards very gradually indeed. 



The lateral processes of the adult sacrum are shown by immature specimens to have 

 various natures. 



Thus we have on each side at first (at the twenty-sixth vertebra) a truly articulated rib, 



Next an anchylosed rib. 



Next a transverse process arising entirely from the neural arch, and much inclined 

 postaxiad (fig. 58, 28, d), 



Next one similar, but smaller (fig. 59, d '), 



Then a shorter, formed by a preaxial process of the centrum and by the parapophysis 

 of the thirtieth vertebra, 



VENTRAL ASPECT OF PELVIS (\ natural size). 

 Fig. 73. 



il 



Letters as before. 



3p2 



