318 NEW YORK STATE MUSEUM 



i 



Aside from the fact that the number of vertebrae in the pelvie 

 sacra vary in Branta, Anser and Chen, the pelves in these three 

 genera of geese exhibit essentially the same general, and in nearly 

 all instances the same special characters. There is very little dif- 

 ference between the pelvis of Anser and the pelvis of Chen, and in 

 Branta the main difference is that the bone is comparatively longer 

 for its width. When considering the skeletons of loons, grebes, 

 mergansers, ducks, geese and swans, I am inclined to think that 

 the greater the number of cervicodorsal vertebrae, associated with 

 the longer and narrower pelvis in any of these forms, the greater 

 is the indication that the species so organized occupy the lower 

 planes in the scale of development. 



Viewing the pelvis of Branta canadensis from above it is 

 to be noted that it has a length of about 17.5 centimeters. Its nar- 

 rowest point is just a little beyond the acetabulae where the bone 

 measures across but 3 centimeters ; while from one antitrochanter to 

 the other it has a width of 5.5 centimeters; its widest transverse 

 diameter being 9 centimeters, it being an interpubic style one, meas- 

 ured at points, on either side, opposite the posterior third of the 

 obturator space. The preacetabular region of this pelvis is very 

 considerably shorter than the postacetabular part, and, as I have 

 just shown, much narrower. In front, the ilia are rounded and 

 narrowly emarginated ; in the median line they completely close over 

 the neural canals, and for their middle thirds they are in contact. 

 Even posteriorly the neural canals have not the barest semblance 

 of any opening. For the most part the external surface of either 

 ilium faces directly outward, but the anteroexternal surface of 

 these bones gradually comes to look directly upward, as in this 

 locality the ilia spread out to cover the heads of the ribs and the 

 diapophyses of the vertebrae. Upon this aspect of the pelvis the 

 outjutting of the acetabulae is very conspicuous, while the hinder 

 thirds of the ischia come plainly into view. Here, in this postace- 

 tabular region of the bone, it will be observed that, save their pos- 

 terior thirds, the ilia are very narrow, and that the main central 

 part of the surface is furnished by the large pelvic sacrum. This 

 gradually narrows from before, backward, being always marked 

 by a double row of interdiapophysial vertebral foramina, the inner 

 rows being only open posteriorly. Instead of being flat, the sacral 

 surface is here concaved, especially in front between the anti- 

 trochanters. Posteriorly, the ilia project beyond the distal extrem- 

 ity of the sacrum for about half a centimeter. Seen upon direct 



