OSTEOLOGY OF BIRDS 



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lateral view the pelvis of Branta offers a number of points of in- 

 terest for examination. Both the internal and external rings of an 

 acetabulum are circular in outline, the diameter of the inner one 

 being considerably less than that of the outer one. A pro pubic 

 spine is present, and the ample antitrochanter faces downward 

 and forward, and slightly outward. Much of the lateral surface 

 of the bone posterior to the acetabulum is absorbed by the enormous 

 ischiac foramen, a vacuity of oval outline, sharp borders, and with 

 a length of 6 centimeters, and an average width of 1 centimeter. 

 The obturator foramen is small and of an elliptical outline, and 

 posteriorly leads into the obturator space by a very narrow strait. 

 This strait may practically be obliterated in Chen and Anser. The 

 obturator space is greatly elongated, and is in the form of a length- 

 ened oval of nearly uniform width. The lower margin of the 

 ischium is sharp, but its posterior fifth is moderately produced 

 downward, and has its edge thickened to articulate with a narrow, 

 elongated facet on the upper edge of the pubic style. This latter 

 rod of bone is very slender as it bounds the obturator space beneath, 

 though it begins to widen slightly as it approaches its ischial ar- 

 ticulation behind, and this widening gradually increases as it passes 

 this point, when its free posterior extremity makes a graceful curve 

 downward and inward, to terminate in a broad, transversely com- 

 pressed, paddle-shaped end. An interval of 2 centimeters separates 

 this from its fellow of the opposite side, both paddles equally pro- 

 jecting to some extent beyond the body of the pelvis posteriorly. 

 The hinder pelvic border is cut squarely across, and a strongly de- 

 fined, deep and narrow ilioischiac notch is present, separating the 

 distal ends of the ilium and ischium of either side, the latter bone 

 being here rather wider than the first mentioned one. Nothing of 

 very marked importance characterizes the ventral aspect of the 

 pelvis of Branta. At the narrow forepart the seven strong pairs of 

 vertebral diapophyses fuse completely by their outer extremities 

 with the nether surface of the ilium upon either side. There are 

 but six of these osseous beams in Chen and in Anser, but apparently 

 seven again in the peculiarly formed pelvis of Dendrocygna. Pos- 

 terior to these the pelvis is narrow and deep, but gradually widens 

 as we pass distad. The transverse processes of the nine last sacral 

 vertebrae are thrown out as braces against the mesial margins of 

 the ilia ; of these the anterior pair are the longest and most dis- 

 tinctly individualized; but after them they gradually shorten and 

 merge with the nether surface of the sacral roof, until the ultimate 



