’ 
SHUFELDT.] OSTEOLOGY OF THE TETRAONIDA. 661 
serving the flight of the ‘‘ Cock of the Plains,” after he has once been 
induced to take wing, will agree that there is anything save an abroga- 
tion of that avian privilege. 
Crania of the North American Tetraonine being placed on the hori- 
zontal plane, as described in my monograph on the osteology of Hre- 
mophila alpestris (Bull. U.S. Geol. and Geogr. Surv. of the Ters., vol. vi., 
No. 1), we observe that their equilibrium is moderately stable, the ante- 
rior bearing point being the tip of the superior mandible, and the two 
posterior bearing points being the external facets upon the tympanics. 
The angles of the foramina magna average 70° while the centrum of 
the parietal vertebra is the chief bone of what here must be the basi- 
cranii, and is found to be nearly in the horizontal plane; the neural 
arch of the occipital vertebra being, as a whole, gently convex out- 
wards and lying in nearly the same plane with the foramina magna. 
The Skull.i—So distinct do we find the hzemal arch of the first cranial 
or occipital vertebra, 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- 
cephalic 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 sitw 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, bo, and po, 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 neutral 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 fontanelle. In 
younger individuals this diamond-shaped vacuity is always present, the 
1The author’s plates and figures illustrating this paper are numbéred in continua- 
tion with others of his published monographs. 
The reader is kindly referred to the foot-note under ‘‘Skull” on page 594 of this 
volume, in my monograph upon the osteology of Speotyto cunicularia hypogea, where 
he will find the author’s remarks upon the theory of the four cranial vertebra, and the 
reasons why they were adopted in certain of his papers. These remarks apply with 
equal force to the present article. 
2 The terms here used for the elements superoccipital, exoccipital, and basioccipital, 
seem to be more or less universally adopted and applied by anatomical writers. Pro- 
fessor Parker and Gegenbaur term the first-mentioned element the supraoccipital 
rather than the superoccipial, as here given. The former of these comparative anat- 
omists says, in his Morphology of the Skull (Lond., 1877, p. 241) in regard to these seg- 
ments as they are found in the chick of the common fowl the second day after hatch- 
ing: “The extensive occipital plane, swelling backwards above, is largely ossified, 
although there are considerable chondrous tracts remaining. The basioccipital ex- 
tends into the occipital condyle, and it is considerably underfloored by the basitem- 
poral plate in front. (Fig. 63.) The exoccipitals ossify the lower half of the sides of 
the foramen magnum. They are very irregular in shape, extending considerably into 
the ear-cartilage. They are perforated by the vagus and hypoglossal nerves. The 
supraoccipital centers have coalesced almost completely to form a large bone bound- 
ing the upper half of the foramen magnum, which is pointed above. Superiorly, the 
margin of the bone is curved like a fan, and abuts on the parietals.” ‘The supraoccip- 
ital centers, according to Professor Parker, are two in number, developing side by side. 
(Op. cit., page 235.) 
