BHUFELDT.] _ OSTEOLOGY OF THE TETRAONIDZ. 673. 
A row of minute foramina encircle the beak anteriorly, where it is the 
thickest, though the segment is non-pneumatic. The general surface 
beneath is depressed below the tomial margins, though it is not very 
extensive, as the wide palatine fissure occupies a good part of the space, 
that terminates anteriorly in a U-shaped curve, opposite the outer nasal 
border. In the Ortigyne the curve of the culmen is more abrupt, 
and the frontals rise above, in some cases even jut over, the premaxil- 
lary. The nasal apertures are also very large and of a shorter elliptical 
outline; the palatine fissure is likewise narrower in comparison, a few of 
which differences are such as one would naturally look for in a bird of so 
near kin, and whose beak has been more than proportionately curtailed. 
On removing the vault of the cranium in an adult female of Centro- 
cercus, SO aS to obtain a free view of the brain-case, we discover the 
usual nervous and vascular foramina present at their most common 
sites, but beyond this we are more struck with the feebleness with 
which many of the salient points are developed, as compared with some 
of the other avian groups; we might sum it up by describing it as a 
lack of angularity and depth. It is true the various fosse are well, 
though not strongly divided, the superior median crest is present, put 
not very prominently developed, and the rhinencephalic fossa is barely 
conical. The section shows the greatest amount of depldéic tissue to be 
in the basi-sphenoid, and bones of the occiput, where for potent reasons 
such material is most urgently in demand. 
In the study of the crania of the adult Tetraonide as an entirety we 
find among the most conspicuous features enlisting our interest the un- 
usual number of bones that remain free in them. The skull can be so 
stripped of its outstanding segments that nothing remains save the 
cephalic casket with the interorbital septum. The rhinal chamber is 
strikingly open, due to the great external nasal passages, and all its in- 
ternal structures, as the ethmo-turbinals, internasal septum, and floor. 
being formed only in cartilage. A pocket existing in the extremity of 
the premaxillary, that fills in with a spongy osseous tissue during life, 
is observed in Centrocercus, which is solid in the Ortygine and Lagopus— 
parial, subcircular pits placed side by side in like locality in Canace 
obscura. 
The orbits are more fortunate in the completeness of their bony in- 
closures—the heavy plate generously extended by the ethmoid to divide 
these cavities very rarely shows any deficiencies. Of all the crania be- 
fore us Canace obscura is the only delinquent in this respect, though no 
doubt this may occur in others. In it quite a vacuity exists near the 
middle of the septum. Anteriorly the prefrontal and frontal throw out 
laterally squamous septa of greater or less completeness, that divide 
these cavities from the common rhinal space. These plates may coa- 
lesce with the processes of the lacrymal, as a rare coincidence, and per- 
chance meet the infraorbital style. The foramina for the passage of 
the optic nerves and the first pair are, as a rule, singularly circular and 
distinct, the minor apertures about them enjoying a like individuality. 
They are noted for their greater size among the Partridges. 
A separate canal is devoted to each olfactory nerve immediately be- 
low the orbital vaults, that usually at its outstart from the cranial end 
has a small opening between it and the one of the opposite side. About 
the entrance to the otocrane we notice principally arounded, squamous 
plate thrown down from above by the mastoid, that is present in all the 
Grouse. vust below and within, this segment also develops a sharp 
spicula of bone, posterior to the tympanic articulation, that evidently 
43 H 
