2^0.2.] SHUFELDT ON NORTH AMERICAN TETRAONIDiE. 337 



coracoids. The shafts are gently curved, of even calibre, and fall nearly 

 directly downwards in some si^ecies, to be slightly exi)anded beneath in 

 order to give better support for the large median dilatation below; this 

 is triangular in outline, thickened in front, sharpened behind. In Ortyx 

 this process is sometimes i)roduced backwards, so as to nearly touch the 

 sternum; this feature obtains, also, among some of the other Quails. 



These bones are all well advanced in ossification in the young chick, 

 but do not develop their distinctive markings until a bird is i^rettj- 

 well along in age; this applies more particularly to muscular lines on 

 the shafts, the base of the coracoids, and the clubbed extremities of the 

 scapulae. In Bonasa, where we noticed how the body of the sternum 

 was narrow like the Quails, we find also the median process of the united 

 clavicles i3roduced backwards towards that bone. This Grousers skeleton , 

 in fact, seems to have the greatest tendency Partridge- ward over any 

 other of the North American Tetraonince. 



The free ossicle of the shoulder-joint, the os humero-scapidare, is not 

 present in any of these birds ; a firm piece of inelastic cartilage seems 

 to supersede it and fulfill a like function. 



The humerus (Plate VII, Pig. 57, H— Pigs. 60, 61 ; also Plate X, Figs. 

 76, 77 of Cupidonia) of Centrocercus is so exceedingly regular that it 

 could be well chosen as the type of that bone in all birds in which it is 

 pneumatic. It is in due proportion for the size of the bird to which it 

 belongs, possessing the usual sigmoidal curves from lateral and superior 

 aspects (we describe the bone in sihi in the closed wing) in graceful, though 

 not decided, prominence. The head or proximal extremity, slightly bent 

 anconad, displays the most usual points for examination about it ; an 

 extensive convex, smooth surface is seen for the glenoidal cavity, below 

 it a deep notch, then the well-defined "ulnar crest" or lesser tuberosity 

 curling over a large sub-elliptical pneumatic foramen, that is so patu- 

 lous that the osseous trabeculae and net- work are plainly seen at its base. 

 The radial crest encroaches but very little upon the shaft, is quite stout, 

 and only at its summit shows any disposition to curve over palmad. 



The shaft is smooth, markedly elliptical on section throughout its ex- 

 tent, and almost entirely devoid of any muscular markings or lines ; it 

 swells gently in the vertical plane as it approaches the distal end of the 

 bone, upon which is placed the ordinary tubercles for articulation with 

 radius and ulna. The inferior condyle, the internal of human anatomy, 

 is the better developed of the two, and the ulnar tubercle is produced a 

 little beyond the bone distally, while the oblique tubercle is brought 

 down on the shaft. The olecranon fossa is rather shallow in the Grouse, 

 being decidedly better shown among the Quails. There are no promi- 

 nent points of diflerence in this bone among the Tetraoninw, except in 

 regard to size; Cupidonia, which has rather a heavy skeleton any way, 

 the humerus is moderately robust in accordance. 



In Odontophorincv the same (characteristics are to be seen; but we dis- 

 cover in addition at the proximal extremity of the bone, on its anconal 

 22 a B 



