SHUFELDT.] OSTEOLOGY OF THE TETRAONID. 695 
this beautiful appendage in this fowl, we find the four coccygeal verte- 
bree very broad and spreading, while the pygostyle is equally exten- 
Sive, being composed of two horizontal plates connected by a vertical 
one, lying longitudinally in the middle plane. The pelvis and the caudal 
vertebre, including the pygostyle in the Guinea Hen, are very much the 
Same pattern as we find them among the Grouse generally, and both this 
bird and Pavo have the characteristic spine protruding anteriorly beyond 
the acetabulum on either side. 
The femur in the young chick of Centrocercus is but partially devel- 
oped; above, the head is almost entirely cartilage, while below the con- 
dyles are very indistinct and the bone bears no signs of pneumaticity. 
In a few weeks, however, these points rapidly exhibit themselves: a 
rounded trochanterian ridge is thrown out; the head essays to assume 
its sphericity; the condyles become evident; the fibular groove appear- 
ing last of all and about the same time with the vascular foramen or 
medullary orifice at junction of upper and middle thirds. In our exam- 
ination of this bone in a fine old cock Cupidonia, and comparing it with 
others, we find that it is remarkably well balanced in point of length 
and general development. 
The trochanterian ridge is prominent and arches over the articular 
facet for the ilium; the neck is distinct and makes an angle of 45° with 
the shaft; the head is well formed, spherical, and in all Grouse seems 
to bear a double depression for the ligamentum teres. Anteriorly below 
the trochanterian eminence there is an extensive collection of pneumatic 
foramina. The “trochanter minor” never develops. 
The shaft is smooth, bent slightly forwards; displays the usual mus- 
cular lines and the medullary orifice; it is nearly cylindrical on section 
about its middle, and before terminal expansion takes place. Below, 
the rotular channel is deeply grooved, separating the prominent con- 
dyles; of these the external and lower one presents the usual fibular 
fissure; behind, the popliteal depression is well sunken, one of the mus- 
cular lines running into it, and often a foramen is found at its base. 
Shallow fosse are found laterally at the outer surfaces of the condylar 
enlargements, and some- 
times a notch where shaft 
meets the internal one ante- 
riorly. The bone is usually 
slenderer in Bonasa, Pedi- 
cecetes, and Canace canaden- 
sis. 
Among the Ortygine the 
femur has the same general 
characteristics; it is, how- 
ever, non-pneumatic, the 
double pit for the ligamen- ~ 
tum teres is better marked, 
and the muscular lines are 
seareely perceptible. 
The patellais never absent 
in the Tetraonida, and occu- 
pies its usual position as a i ae 
free bonelet protecting the anterior aspect of the knee-joint. It aveom- 
modates itself to the conformation of the rotular channel, having a flat- 
tened surface superiorly, a rounded border below, and a double surface 
behind, the most extensive aspect of which is applied to the side towards 
the internal condyle. 
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