STUDIES OF THE MACROCniRES. 



315 



sternum may sometimes assume a different form even for the 

 same species *, which T have never found to be the case in the 

 pelvis. 



In PL XYIII. fig. 7 is represented the superior or dorsal 

 view (double the size of life) of the pelvis of Ampelis cedrorum j 

 it shows very well indeed the general form and characters of this 

 bone as it occurs among the Passeres. Considerable interest 

 attaches, however, to an examination of a transition series of 

 pelves through the Passerine group of birds into other orders 

 wherein marked differences are to be found. 



Now in such a bird as IIarporhy7ichus ritfus, for instance, or 

 any of its genus, the pelvis, when viewed from above, has pretty 

 much the same form as it has in Ampelis ; but all the processes 

 are more prominent, and all the ridges and crests more con- 

 spicuous and defined. This lends to the bone quite a striking 

 appearance in these higher Thrushes. But as we pass through 

 the members of the Oscinine group and into the Clamatores, this 

 bone, altliough it retains its general pattern, gradually loses 

 this peculiar angularity, and gains in breadth while it becomes 

 comparatively shorter in the longitudinal direction. My meaning 

 will be made clearer when we come to examine, further on, the 

 pelves of the Swallows and Swifts. 



As to the characters of the pelvis in Ampelis, we are to note 

 that, anteriorly on its dorsal side, the inner margins of the ilia 

 are widely separated from the crista of the sacrum ; that tlie pre- 

 and post-acetabular areas are about of equal dimensions, that the 

 former are concave outwards, while the reverse condition obtains 

 with the latter; that the " sacrum " upon this view is roughly 

 lozenge-shaped, and that interapophysial foramina of varying 

 sizes may be found to exist in it. 



Upon the lateral aspect it is to be observed, that not only is 

 the acetabulum (as it invariably is in birds, I believe) completely 

 surrounded by bone, but the ischiadic, the obturator, and the 

 obturator space are true foramina, or at least are entirely en- 

 circled by bone. In Tijrannus verticalis the ischium fails to 

 meet the post-pubis between the obturator foramen and obturator 



* For examples of this see my remarks upon the different forms of sternum 

 in the Oathartidae, " Osteology of the Cathartid;e," in Contributions to the 

 Anat. of Birds, from U.S. Geol. and Geog. Survey, 1882 (Hayden's 12th 

 Annual), pp. 771, 772, where four figs, of sternum of C. aura are given. 



LINN. JOUEN. — ZOOLOGY, VOL. XX. 25 



