SKELETON OF PHORORHACOS INFLATUS. 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” vertebre being very large and projecting far below 
the edges of the ilia. The anterior renal fossee 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 fosse which, as in Rails 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 vertebre unite with it, while in the fossil there are 
six or seven such vertebre. 
The Ilium. (Plate XVI., 7.) 
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., 7s.) 
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 turther back than the ilio-caudal process, 
