SHUFELDT.] OSTEOLOGY OF THE TETRAONIDZ. 693 
and including the sacrum forms a gently convex surface; the “ gluteal 
ridges” dividing these two regions commence with the anterior iliac 
borders and are conveyed clear round to form the posterior ones of the 
same bones, describing two great Ss, the lower and outer curves of 
which pass by the acetabular projections, points where in some birds they 
terminate. 
Among the principal features to be noted in a Jateral view is that 
the shaft of the pubis is in nearly all instances free from the ischium 
after quitting the cotylis and forming the elliptical obdurator foramen. 
If it anchyloses with this bone at all it usually occurs just behind that 
orifice. 
The ischium overlaps the pubis at two points—one quite broadly near 
its middle, and, again, by a process at its outer and inferior angle. 
The “ischiatic foramen” is the largest vacuity of the group of three 
that here present themselves; its boundary is sub-elliptical, with its 
major axis depressed posteriorly if it were produced. 
Both the internal and external margins of the cotyloid cavity, or ring 
rather, are circular, the former of which is not a little smaller, thus 
affording a very good and quite extensive surface for the head of the 
femur; the anti-trochanterian process or facet directed backwards is 
likewise ample, so that the femora are well supplied with articulating 
surfaces. 
There seems to be among the Grouse a predisposition for the ilia to 
overhang the region of the ischiadic foramina; it is most successfully 
carried out in Cupidonia. Viewed from below, we are struck with the 
amount of room and space these combined bones inclose; the profundity 
of the pelvic basin. This is very much enhanced by broad reduplica- 
tures of the ilia and ischia 
behind, and a general 
though even constriction of 
a prominent rounded border 
or rather ridge that extends 
from the fourth diapophysial 
abutment of the vertebra 
against the ilia on either side 
to the outer angles of the 
ischia. Within, too, we often 
find about and at the base 
of theseiliac fossz apertures 
for the entrance of air into 
these bones; such pneumatic 
foramina are also seen be- 
yond the os pubis and below 
the cotylis on either aspect. 
The pubic extremities 
never meet behind, though 
in many species they are 
very long and usually take 
the curve given them by the 
ischia just before leaving 
these bones. Their distal 
extremities are flattened in 
Centrocercus and generally more expanded than among the other varie- 
ties. 
The pelvis of Cupidonia is so different from the general description 
we have just given, that the author feels justified in giving his reader 
Ortyx virginiana. 
