PELVIC ARCH OF HESPERORXIS. 



The three pelvic bones of Hesperomis are firmly coossified, as in 

 existing birds, but the ilium is ankylosed to the sacrum in the acetabular 

 region alone. The true pubic element, or " ilio-pectineal " process, is not 

 larger than in many recent birds, and is much inferior in size to the 

 corresponding- protuberance in the pelvis of Geococcyx, and of Tinamas, 

 shown below. 



In these two genera, moreover, another point of resemblance to 

 Hesperomis appears in the acetabulum, the inner margin of which is 

 materially narrowed by ossification, although a large perforation remains. 

 In Hesperomis, the acetabular foramen is much smaller than in any 

 known bird, and during life was doubtless closed by the round ligament. 

 This reduction of the acetabular opening by ossification strengthens the 

 pelvis at this point, and thus is of service where powerful action of the 

 posterior limbs is required. 



Figure 19. — Pelvis of Geococcyx Californianus, Baird ; seen from the left ; naturals 



Figcee 20. — Pelvis of Tinamus robuslus, Sclater and Salvin ; seen from the left; natural size. 

 a. acetabulum ; il. ilium ; is. ischium ; p. pubis ; p'. postpubis. 

 10 



