.Vo. 3.] SHUFELDT ON NORTH AMERICAN TETRAONID^. 311 



Vertebrates lie seems to accuse the Struthionidcv alone of this singular 

 feature, or at least "those birds in which the power of flight Is abro- 

 gated." Kow, such of my readers as have had the opi^ortunity of ob- 

 serving the flight of the " Cock of the Plains," after he has once been 

 induced to take wing, wiU agree that there is anything save an abroga- 

 tion of that avian privilege. 



Crania of the North American Tetraonince being placed on the horizon- 

 tal plane as described in ray monograph on the osteology of Ercmophila 

 alpcstris (Bull. U. S. Geol. and Geogr. Surv. of the Ters., vol. vi., No. 1), 

 we observe that their equilibrium is moderately stable, the anterior 

 bearing point being the tip of the superior mandible, and the two pos- 

 terior bearing i)oints being the external facets upon the tympanies. 

 The angles of the foramina magna average 70° while the centrum of the 

 j)arietal vertebrje is the chief bono of what liere must be the basi-cianii, 

 and is found to be nearly in the horizontal plane : the neural arch of the 

 occipital vertebrse being, as a whole, gently convex outwards and lying 

 in nearly the same i)lane with the foramina magna. 



The SlculL* — So distinct do we find the hiiemal arch of the first cranial 

 or occipital vertebrae, and fulfilling such a diverse end, with its ap- 

 pendage the pectoral limb, in birds generally, that its description will 

 be undertaken further on under the subject of the "scapular arch" and 

 our attention be engaged at this point only with the neural or epen- 

 cepahlic arch of this segment of the cranium. 



The primoidal elements of this, the superior arch of the vertebra in 

 question are seen to a greater or less extent in situ in the young and 

 "bird of the year" of Centrocercus in Plate V, Figs. 47-50, and in the 

 disarticulated skull of the same. Fig. 51, as so, eo, ho, and j;o, lettering 

 respectively the essential elements " superoccipital," "exoccipital" (the 

 parial bone and counterpart of this segment being intentionally omitted, 

 as are the duplicates of other segments), "basioccipital," and the con- 

 nately developed process "paroccipital" of the neurapophyses. 



In Sage Cocks the size of those figured in Plate V, Figs. 50 and 51, 

 we find the neural spine of the first vertebra, so, to be a light, spongy 

 bone, one and a half centimeters wide by about one-half of a centimeter 

 deep — covered with a thin layer of compact substance. Its upper border 

 displays in the median line a demi-lozenged shaped notch that when 

 the bone meets the parietals, which latter have their posterior and inner 

 corners deficient, forms in many birds of this age a "fontauelle." In 

 younger individuals this diamond-shaped vacuity is always present, the 

 " anterior foutanelle" being formed in them in a similar manner, though 

 narrower and longer, between the frontals and parietals. The lower 

 border of the superoccipital i^resents a smooth, angular depression, that 

 in the articulated vertebra goes to complete the superior third of the 

 foramen magnum. 



* The authors plates aud figures illustrating this paper are uumbered in coutinua. 

 tioD with others of his published monograiihs. 



