170 MR. W. K. PARKER ON THE OSTEOLOGY 
Example 2. Oreophasis derbyanus. 
This is an extremely interesting form of Gallinaceous bird, and serves to connect 
the typical subfamily with the Guans and Curassows, through the African genus 
Numida. It might be supposed that the two genera Oreophasis and Numida were 
merely isomorphs: but that is not the whole of the matter; they come very close 
together in structure. This bird is about one-fourth larger than the Guineafowl and 
Gamecock, and its bones are relatively, as well as really, less spongy and thick than 
those of Orax globicera. In the trunk, the last or compound caudal vertebra contains 
fat, and so does the furculum and all the limb-bones save the humeri; the other bones 
contain air. The Oreophasis is therefore intermediate between Gallus and Craz in this 
respect; for in the former the scapula contains fat, in the latter the thigh-bones contain 
air. Both Oreophasis and Numida agree with Crax in having the occipital condyle 
typical, but the occipital plane less vertical and more rounded than in the large typical 
forms ; they both agree in the nearly typical condition of the basitemporal region and 
the tympanic cavities. ‘There is a beautiful gradational series, in the Fowl-tribe, of © 
the degrees in which the incudal crura (heads of the ‘‘ os quadratum’’) are collapsed 
or fused together. 
In the Common Fow! the single head of the great incus has a kidney-shaped articular 
surface for the squamosal, and a small oval facet for the prootic ; and in front of this is 
a trochanter-like tubercle, which might easily be mistaken for the missing head, but 
which is either abortive or missing in typical birds, where the heads are very distinct. 
In the Turkey, the Cock of the Woods, and the Red Grouse, the prootic facet is also very 
small, and in the latter bird is apt to become fused with the outer facet; but the con- 
cavities in the side of the skull are very distinct. In Numida meleagris the inner facet 
is still small, but is more distinct from the outer ; whilst in Oreophasis, as in Crax and 
Talegalla, the inner or posterior head reaches the opisthotic region: in typical birds 
it goes still further back, and articulates at times with the exoccipital. The head of 
Oreophasis is in advance, histologically, of the typical Gallus and Numida ; its texture is 
more like that of the skull in the higher sorts of birds. The frontals, instead of being 
outspread as in Crax, are mysteriously drawn upwards into a large bony horn-core, 
which has a slightly backward turn, but which is much more vertical than the horn- 
core of Numida: it is also nearly circular in outline, and not pinched from side to side 
as in the Guineahen. More than the upper half of the suture exists in this process, 
and in front below the suture there is a shallow fossa, gradually widening into the con- 
cave anterior frontal region: this sulcus is divided into two by a ridge, and on each 
side there are two more sulci, which become one opposite the suture. These sub- 
parallel grooves and ridges, gently converging upwards in the front of the horn-core, 
make it a very elegant structure. In section, the internal coadapted walls of the 
halves of the process are seen to be perfect ; and they are each filled with moderately 
fine diploé. Another large pair of sulci exist close to the posterior face of the process: 
