No. 2.] SHUFELDT ON NORTH AMERICAN TETRAONIDJE. 32 1 



between the out-turned frontals, the culmen of tins bone slopes by a 

 gently increasing arc to tlie tip of tlie beak. This surface is rounded 

 and split in two from the enlarged inner extremity to a point over the 

 distal border of the nostril ; this division lasts during life. Tlie exter- 

 nal nasal orifices are unusually large and sub-elliptical in outline. The 

 head of the ethmoid shows in very young chicks, but is even ti> ally cov- 

 ered by this bone, which also fills in snugly the interuasal space (Plate 

 X, Fig. 73). 



The osseous maxillary tomia are even sharper than when they -were 

 capped with the horny integumental sheath that the entire bill wears 

 during life; they are produced backwards on a triangular process of the 

 bone below the shaft of the maxillaries, touching them in the Quails. 

 A row of minute foramina encircle the beak anteriorly, where it is the 

 thickest, though the segment is non-pneumatic. The general surface 

 beneath is depressed below the toniial margins, though it is not very 

 extensive, as the wide i)alatine fissure occupies a good part of the space, 

 that terminates anteriorly in a U-shaped curve, opposite the outer nasal 

 border. In the OdontopJiorince the curve of the culmen is more abrupt, 

 and tlie frontals rise above, in some cases even jut over, the i)remaxil- 

 lary. The nasal apertures are also very large and of a shorter ellipti- 

 cal outline; the palatine fissure is likewise narrower in comparison, a 

 ■few of which differences are such as one would naturally look for in a 

 bird of so near kin, and whose beak has been more than proportion- 

 ately curtailed. 



On removing the vault of the cranium in an adult female of Centra-- 

 eercus, so as to obtain a free view of the brain-case, we discover the^ 

 usual nervous and vascular foramina present at their most common 

 sites, but beyond this we are more struck with the feebleness with 

 which many of the salient points are developed, as compared with some- 

 of the other avian groups ; we might sum it up by describing it as a 

 lack of angularitj'" and depth. It is true the various fossae are weU, 

 though not strongly divided, the superior median crest is present but 

 not very prominently developed, and the rhinencephalic fossa is barely 

 conical. The section shows the greatest amount of deploic tissue to be 

 in the basi-sphenoid, and bones of the occiput, where for potent reasons, 

 such material is most urgently in demand. 



In the study of the crania of the adult Tetraonidce as an entirety we 

 find among the most conspicuous features enlisting our interest the un- 

 usual number of bones that remain free in them. The skull can be so 

 stripped of its outstanding segments that nothing remains save the 

 cephalic casket with the interorbital septum. The rhinal chamber is 

 strikingly open, due to the great external nasal passages, and all its 

 internal stiiictures, as the ethmo-turbinals, interuasal septum, and floor 

 being formed only in cartilage. A pocket existing in the extremity of the 

 premaxillai'y, that fills in with a spongy osseous tissue during life, is 

 observed in Centrocercus, which is solid in the OdontophorincB and Lago- 

 21 a B 



