AXIAL SKELETON OF THE OSTRICH. 431 



traces of diapophysial and parapophysial prominences. The neural spine is more or 

 less trifid at its distal end (fig. 68, ns). 



The postaxial surface of the centrum is decidedly concave. 



The vertebra often becomes anchylosed with the next and last, both by its centrum 

 and the distal portion of its spine. 



The Fifty-sixth Vertebra. 



This vertebra has no neural arch and no transverse process (fig. 69). 



It is a dorso-ventrally extended lamina of bone, extremely compressed laterally, with 

 a very irregular, generally more or less rounded, margin dorsally, ventrally, and post- 

 axially. It often anchyloses with the preceding vertebra at the dorsal and ventral parts 

 of its preaxial surface, or rather margin, thus producing a foramen which looks from 

 side to side. 



The existence of another (but minute) foramen placed postaxially to that just 

 described may indicate that this bone really consists of two or more vertebrae fused and 

 anchylosed into one osseous mass. 



Sometimes a little bridge of bone (fig. 69, d) connects its centrum, laterally, with the 

 centrum of the fifty-fifth, or ninth caudal, vertebra. 



THE PELVIS. 



This enormous bone consists of no less than twenty-two vertebrae, more or less com- 

 pletely anchylosed together (in the adult), and with the two ossa innominata, which latter 

 thus cannot conveniently be excluded from the description of the axial skeleton. 



PreaxiaUy the sacrum exhibits the preaxial surface of the first sacral vertebra (with 

 characters corresponding with the vertebra naturally preaxiad to it) roofed over by the 



PREAXIAL ASPECT OF PELVIS (i natural size). 

 Fig. 70. 



ut, antitrochanteric process : i and i', ischium ; )'/, ilium ; p, pubis ; pi, rib ; s, spinous process of postanterior 



vertebrae ; sy, pubic symphysis. 



two iliac bones {il), which meet together over the dorsal end of its spine and diverge 

 ventrad at an angle of about 63° — the two diverging lines being carried on by the two 

 anchylosed ribs {pi) of the first sacral A^ertebra. 



