72 ODOXTORXITHES. 



The Pubis. (Plates X and XL) 



The bone usually called "pubis" in modern birds, which the writer 

 has shown to be probably the post-pubis, forms, in Hesperomis, the lower 

 posterior portion of the acetabulum, and then extends backward as a 

 long, slender, rod-like bone, nearly parallel with the ischium. It is some- 

 what long'er than the ischium, and its distal extremity is truncated at right 

 angles with the shaft. This bone is of nearly equal width throughout its 

 entire length, and sends off no processes or projections toward the ischium, 

 or from its own lower margin. 



Viewed from the inner side, the bone above described is seen to pass 

 beneath the acetabular foramen in a strong ridge, and terminate in front 

 of the acetabulum, in an obtusely rounded tuberosity. This process may 

 be seen in some recent birds, more particularly in those that especially use 

 their posterior limbs. It has been called the ilio-pectineal process of the 

 ilium, and is considered an outgrowth of that bone. The writer has shown, 

 however, by a comparison of the pelvic elements in Dinosaurian reptiles 

 and in birds, that this prominence should be regarded rather as probably 

 representing the pubic bone of reptiles. 1 



The relation of the principal pelvic elements to each other in the 

 pelvis of recent birds is illustrated in the figures given on page 71. In the 

 pelves represented on page 73, the remnant of the reptilian pubis is still 

 plainly to be seen, especially in Geococcyx. It is not improbable that the 

 retention of this process may be due in part to the habits of certain species, 

 as it seems to be best developed in running birds, and those that especially 

 use the posterior limbs. A similar process is seen in some mammals, 

 where it may serve a like piupose. 



The outer surface of the pelvis in Hesperomis, especially of the ilium, 

 is marked by delicate vascular impressions, but the bones themselves are 

 dense, and nearly solid. 



1 American Journal of Science and Arts. Vol. xvi, p. 415, Nov., 1878; and vol. 

 xvii, p. 92, Jan., 1879. 



