SKELETON OF PHOEOEHACOS LNTLATUS. 75 



Posteriorly the pelvis ends in the sharp hinder angle of the ischium, which is separated 

 by a semicircular bay from the ilio-caudal process of the ilium. 



Seen from below (Plate XVI. fig. 3) the narrowness of the pelvis is even more 

 noticeable than in the dorsal view. There is practically no internal iliac fossa, the 

 centra of the anterior " sacral " vertebrae being very lai'ge and projecting far below 

 the edges of the ilia. The anterior renal fossae are extremely narrow, and are scarcely 

 visible from this point of view ; they are separated by the processes of the two sacrals 

 from the enormous posterior renal fossa? which, as in Eails and some other birds, are 

 prolonged backward into long pocket-like extensions, floored by an ingrowth of the 

 ilium. The only bird in which this ventral ingrowth of the ilium is developed to 

 anything like the length seen in Phororhacos is Fulica, in which the broad transverse 

 processes of three or four urosacral vertebrse unite with it, while in the fossil there are 

 six or seven such vertebrse. 



The Ilium. (Plate XVI., il.) 



In its pre-acetabular region the dorsal border of the ilium is convex, the ventral 

 concave, and in front the two are united by a nearly straight anterior border which is 

 slightly inclined forward. The ilio-pectineal process is broken, but seems to have 

 been small. 



As already mentioned, the postacetabular region is considerably longer than the 

 pre-acetabular, from which it is sharply separated by the supra-trochanteric crest. It 

 is nearly equal in width throughout its length. Posteriorly it terminates in the 

 prominent ilio-caudal process, the lower part of which, however, may be formed by 

 the ischium : from the end of this process runs a ridge which seems to mark the 

 junction of the two bones, and certainly is continuous in front with the suture 

 between them. A second ridge, commencing at the hinder border of the bone close 

 to its sacral border, runs forward and then downward to join that just described 

 close to the ischiadic foramen. 



The Ischium. (Plate XVI., is.) 



The share which this bone takes in the formation of the acetabulum cannot be 

 determined, owing to the complete fusion of the pelvic elements in that region. 

 Beneath the ischiadic foramen it forms a bar of bone 15 mm. wide, which, near its 

 proximal end, bears on its ventral edge a short, stout process which touches the pubis, 

 thus enclosing an obturator foramen. Beneath the ischiadic foramen the ischium 

 expands into a broad plate of bone, the outer surface of which is concave from 

 above downward, and the inner traversed by a prominent rounded ridge marking 

 the prolongation of the axis of the bone. The upper edge unites closely with the 

 ilium, the lower curves downward and outward and terminates posteriorly in an 

 angular process which projects slightly further back than the ilio-caudal process. 



