170 MR. W. K. PARKER ON THE OSTEOLOGY 



Example 2. Oreophasis derbyanus. 



This is an extremely interesliag 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 Crax globicera. In the trunk, the last or compound caudal vertebra contains 

 fat, and so does the furculura and all the limb-bones save the humeri ; the other bones 

 contain air. The Oreophasis is therefore intermediate between Gallus and Crax 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 basiteinporal 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 Fowl 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 diploe. Another large pair of sulci exist close to the posterior lace of the process : 



