1888. J PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



225 



common neural spine of the leading vertebrae, converting the ilio-neural 

 grooves into canals. 



Each preacetabular portion of an 

 ilium is much shorter than its post- 

 acetabular part, and also on a very 

 much lower level. In front its bor- 

 der is emarginated, transversely 

 truncate, and somewhat serrated. 

 The surface of the bone is concave, 

 and for the most part looks upward 

 and outward. 



Behind the acetabulum most of 

 the ilium is devoted to the lateral 

 aspect of the pelvis. 



Turning to this side of the bone, 

 we notice a pro-pubisof considerable 

 size in front of the cotyloid ring, 

 while the post-pubic element is a 

 long slender rod, extending directly 

 between the under side of the ob- 

 turator foramen and the postero- 

 external angle of the ischium, with 

 which it articulates. Beyond this, it 

 trebles its width and curves rather 

 abruptly toward the fellow of the 

 opposite side. A very narrow, open 

 strait connects the obturator fora- 

 men and the obturator space; the 

 former being rather smaller than 

 usual and the latter very large. 



The lower margin of the ischium 

 is concave downward and very sharp, 

 while the posterior border of the 

 pelvis, formed by both the ischium 

 and ilium, is perpendicular to the 

 long axis of the bone. It shows one 

 or two indentations that are not to 

 be found in the same pelvic border 

 of the Eider. 



The acetabulum is large, with its 

 inner and outer rings nearly of the 

 same size; an autitrochanter of mod- 

 erate dimensions stands between it 

 and the antero-superior margin of 

 the large elliptical ischiac foramen. 



Posterior to this latter aperture the ilium rises as a smooth dome 

 Proc. N. M. 88 15 JtU**UW.,l**'l- 



Fig. 6. Eight lateTal view of pelvis, caudal 

 vertebra, and sacral ribs of Mergus scrrator ; 

 life size. By the author, from specimen 16626, 

 Smithsonian collection. 



