SHULELDT J OSTEOLOGY OF THE TETRAONIDZ. 697 
oblique ligament that is attached higher up on the inner aspect of the 
shaft, that also holds some of the extensor tendons in position. The 
condyles in mature birds have an antero-posterior position at the 
extremity of the tibia; these are of a uniform outline, and the inter-con- 
dyloid notch that separates them is of no particular depth until it arrives 
on the anterior aspect of the bone. Externally and laterally almost 
within the limits of the outline of the outer condyle we find two tuber- 
cles, one above another; the lower is for ligamentous attachment, the 
upper is the remnant and only existing evidence of the lower extremity 
of the fibula. A similar tubercle is found on the opposite, side corre- 
sponding to the lower one just described on the cuter aspect. 
The jibula is freely de- 
tached and never completely 
anchyloses with the tibia. 
Its proximal extremity is 
clubbed, enlarging very ae 
much as it rises above the ~ 
condylar surface of its com- < 
panion from the fibularridge; 
it is laterally compressed and .\ 
convex above at the summit. \; 
In many Grouse the attenu- -s 
ated remains of itsextension ~ 
below can be traced on the 
shaft of the tibia, which bone 
has nearly absorbed this 
third of its weaker associate. Callipepla squamata. 
In the early life of the chick of the Grouse we have been discussing, 
the combined tarsals are surmounted by a third plate of cartilage, that 
subsequently ossifies, apparently by one center. The bone thus formed, 
the centrale, we believe undoubtedly to represent either a single tarsal 
element or the connate bones of the second row. 
At this age the metatarsals that combine to form the shaft of the 
tarso-metatarsus are still easily individualized, though well on the road 
toward permanent fusion. It will be observed that we still retain the 
term tarso-metatarsus, and we think justly so, as the compound bone of 
the mature bird has combined with it at least one of the tarsal bones. 
The tibia could with equal reason be termed the tibio-tarsus, and again 
the compound bone in manus, the carpo-metacarpus, but for obvious 
reasons such innovations are not always advisable. 
We discover in Centrocercus and Canace canadensis—in that strong 
inelastic cartilage that is found at the back of the tarsal joint in all the 
Grouse, on the inner side—a concavo-convex free bone, nearly a centi- 
meter long in the Sage Cock, and two or three millimeters wide; this 
ossicle must be regarded only as a sesamoid, though it is nearly as large 
as the patella, and in no way as constituting one of the tarsal bones. 
It will be remembered that in the first edition of my monographs 
upon the osteology of Speotyto and Hremophida, the old term of the “ cal- 
caneal” process was retained for that prominent projection found at the 
superior and hinder end of the bone tarso-metatarsus. It having any- 
thing to do with the caleaneum or the os calcis in the homologies of the 
avian tarsus, was stoutly denounced in the first appearance of my mon- 
ograph upon the osteology of the North American Tetraonide. In these 
papers, as well as in my osteology of Lanius ludovicianus excubitorides, it 
was given the name of the tendinous process, from the well-known fact 
that by one means or another it’ transmitted the flexor tendons at the 
