320 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [For. vi. 



lamella, twisted upon themselves in a manner to conform with the 

 superior base of the beak, overlap the frontals as already defined, are 

 separated from each other by the intermaxillary, throwing out below to 

 meet this bone a sharp process, thus forming a broad elliptical bound- 

 ary limiting the capacious osseous nares. In all adults of this family 

 they are easily detached by maceration. These bones are well shown 

 in Plate X, Figs. 71 and 73, in the cranium of Cupidonia, from an un- 

 usually fine bird sent with a number of others, for which our thanks are 

 graciously tendered to Captain Eichards Barnett, Medical Department 

 United States Army. It will be observed that the bone becomes so at- 

 tenuated in some specimens as to give rise to a foramen, as seen in the 

 latter figure. The haemal arch is ycleped " maxillary," as its lower rib 

 and spine constitute the major share of the superior mandible or maxilla. 

 The pleurapophyses seen in the palatines are long, rib-like bones with 

 their anterior ends much flattened from above downwards, to fit into a 

 fissure on either side made for them in the intermaxillary below the 

 maxillaries. I^ear their middles they curve moderately outwards to de- 

 velop compressed heads at their posterior extremities, fitting into a 

 notch in either i)terygoid, and concave mesially for the rostrum of the 

 basi- sphenoid. 



At their inner thirds they send off thin sheets of bone that curve up- 

 wards, barely to touch the ramphosial process of the sphenoid, accom- 

 panying it as far as it extends distad, then sloping away on the ribs of 

 the bones themselves. The haemapophysial maxillaries are elements 

 that seldom change their ornithic characters, and in Tetraonidm seem 

 to be reduced to their simple typical form — in completing the delicate 

 infraorbital bar on the one hand — and just previous to becoming wedged 

 into the premaxillary above the palatines, dispatching a bony offshoot 

 on either side nearly to meet each other in the palatine fissure on the 

 other. 



The remaining pair of bones found at the inferior aspect of the birds' 

 skull are the pterygoids. In the Grouse they are stumpy, subcompressed 

 concerns, with half -twisted shafts, having broad concave surfaces for 

 the facets on the rostrum, which are notched distally for the reception 

 of the palatines. The articulation with the tympanies is equally exten- 

 sive, monopolizing long, narrow facets beneath the orbital processes on 

 those bones. 



We have arrived finally at the point in our descriptive skeletology of 

 the avian skull, where we have to deal with the anterior and ultimate 

 haemal spine, here fulfilling most important functions as the superior 

 mandible, as it does throughout the class at large. In Tetraonidw, as 

 in the vast majority of birds, the intermaxillary or the "premaxillary" 

 of some authors is of much stouter material than most other bones of 

 the head, its use, being a very obvious reason for this. (Plate V, Fig. 

 51, N". Pf. mx, i.mx.). 



From the moderately free fronto maxillary and pseudo hinge-joint, 



