OSTEOLOGY OF BIRDS 



203 



The form of the broadened V of the os furcula in those two birds 

 is almost identical, but the hypocleidium of that bone in Tym- 

 panuchus is far larger than it is in G . b a n k i v a . 



I have carefully examined and compared skeletons of the species 

 and subspecies of the genus Pediocaetes, and several of the char- 

 acters they present are already given above. In Pediocaetes 

 p h a s i a n e 1 1 u s c o 1 u m b i a n u s the skull, sternum and limb 

 bones essentially agree with the corresponding structures in our 

 other typical grouse, and I have already stated that in the matter 

 of its pelvis, ribs, and vertebral column, it is at variance with them, 

 and in those particulars more nearly like Tympanuchus. 



Pecliocaetes is remarkable for having" a comparatively long 

 femur, and a relatively short tibiotarsus. This character is also 

 apparent in species of Tympanuchus, though not quite so well 

 marked. It is also more or less evident in Bonasa and other forms. 

 The os furcula of Pediocaetes is deserving of a passing word, for 

 although it has the general galline pattern, it is nevertheless char- 

 acterized by the shortness of its clavicular limbs and its long and 

 narrow hypocleidium, which latter lies nearly in the same plane with 

 the former. 



A splendid example of the gallinaceous skeleton is seen in that 

 of Centrocercus u r o p h a s i a n u s [pi. 2, fig. 14, 15, 16 ; 

 pi. 7, fig. 31], the Sage cock of the western plains. I have killed 

 scores of those .noble birds, and taken them at all ages. In con- 

 sequence a fine series of their skeletons is before me at the present 

 writing. 



The cranial portion of the skull in an old Sage cock [pi. 2, fig. 14] 

 is massive and dense, and the basis cranii with the plane of the 

 foramen magnum face more directly posteriorly than is the rule 

 among our grouse. Shell-like and capacious tympanic bullae sur- 

 round large aural apertures, one upon either side. At the side of 

 the skull the long, acute, and lamelliform squamosal process is con- 

 spicuous ; and at its outer edge, rather above its middle, there fuses 

 with it the end of the postfrontal apophysis. The two surround 

 an elliptical foramen. The interorbital septum in this bird is usu- 

 ally nearly or quite entire, and the pars planae are fairly well de- 

 veloped. In the facial region, the combined premaxillaries remain 

 more or less free from the other bones of the face throughout life. 

 External narial apertures are conspicuously large, and the rhinal 

 chambers ample and much exposed in the dried skull. Anteriorly, 



