jro.2.] SnUFELDT ON NORTH AMERICAN TETPA0NIDJ3. 321 



between the out-turned frontals, the culmeu of this bouc slopes bj' a 

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

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

 distal border of the nostril 5 this division lasts during life. The exter- 

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

 head of the ethmoid shows in very young chicks, but is eventrally cov- 

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

 X, Fig. 73). 



The osseous maxillary tomia are even sharper than when they were 

 capped with the horny iiitegumental 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 tomial margins, though it is not very 

 extensive, as the wide palatine fissure occuiiies a good part of the space, 

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

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

 and the frontals rise above, in some cases even jut over, the premaxil- 

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

 cal outline ; the i)alatiue fissure is likewise narrower in comparison, a 

 few of which diiierences 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 Centro- 

 cerciis, 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 bej'ond this we are more struck with the feebleness with, 

 which many of the salient points are developed, as comi)ared with some- 

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

 lack of angularity and depth. It is true the various fossae are well, 

 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-si)henoid, and bones of the occii)ut, where for potent reasons 

 such material is most urgently in demand. 



In the study of the crania of the adult Tetraonidw 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 M-ith the iuterorbital septum. The rhinal chamber is 

 strikingly oi)en, due to the great external nasal passages, and all its 

 internal structures, as the ethmo-turbinals, internasal septum, and floor 

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

 premaxillary, that fills in with a spongy osseous tissue during life, is 

 observed in Centrocercus, which is solid in the Odontophoriiia' and Lago- 

 21 a B 



