666: GEOLOGICAL SURVEY OF THE TERRITORIES. 
tubes, that add to the parietes of the entrance of the otocrane. Below 
and superiorly, at the base of the junction of the two bones, we find the 
carotid foramina, with a depression between them mesially, and still 
lower down, slightly protected by an attenuated offshoot from beneath, 
the separate apertures of the anterior and buccal entrances of the Eus- 
tachian tubes. 
The remaining surface, unbroken in character, extending posteriorly, 
goes to complete the basi cranii. The coaptation of the elements form- 
ing the neural arch of the parietal vertebra is shown in Plate V, Figs. 
47-50, their amalgamation in the adult in Plate VI, Fig. 52. 
The chief importance of the hemal arch of this vertebra depends 
upon the bony support it affords the tongue. In a fine specimen of an 
adult Lagopus leucurus, kindly presented me by Mr. Robert B. McLeod, 
then residing in Leadville, Colo., we find the following characteristics 
presented to us for examination, and they extend with little deviation 
to all the members of the family. The hyoid arch! consists of, in the 
specimen under consideration, seven bones. The confluent ceratohyals 
and glossohyal, which latter is largely completed anteriorly by cartilage, 
form one segment; the ceratohyals diverge from each other smartly 
behind, and at their point of meeting afford the facette for the trans- 
verse trochlea surface on the basi-hyal. This last bone, the second in 
order, measures half a centimeter in length, being enlarged at both ex- 
tremities, flattened from above downwards, the anterior end being fash- 
ioned to fulfill the purpose already mentioned, while the posterior and 
larger extremity presents two facettes, looking backwards and outwards, 
to articulate with the hypobranchial elements of the thyro-hyals. The 
third segment also meets this compound articulation at this point, a 
short urohyal, it, too, being completed at its posterior extremity by car- 
tilage. The hypo- and cerato-branchial elements of the thyro-hyals make 
angles with each other and curve upwards in conformity with the basi- 
cranii. 
The sub-cylindrical hypo-branchials are one and a half centimeters 
long, and connected with the posterior elements by quite along and in- 
tervening piece of cartilage of the same caliber; the smaller cerato- 
branchials also taper off behind with the same material. 
This arch in the Tetraonide long remains almost entirely cartilaginous, 
the hypo-branchial elements alone being composed of bone, and a bird 
must. be of quite an advanced age before he can boast of a complete 
osseous framework as forming a component part of his lingual apparatus. 
The neural arch of the third cranial vertebra now to be defined is the 
prosencephalic—its hemal arch the “mandibular,” as its hemapophy-. 
sis constitutes the lower jaw, termed “‘ mandible,” in avian skeletology. 
The fusing of the centrum of this segment with the basi-sphenoid has 
already been elucidated; the rostrum thus formed is gently inclined 
upwards and forwards, grooved along its entire superior aspect, tapering 
to asharp point anteriorly to receive the connate prefrontals in the bony 
gutter at its distal third. Beneath it displays towards its base the 
1In speaking of this compound bone, Professor Gegenbaur tells us: ‘‘Two pairs of 
arches can be made out in birds. The rudimentary first arch fuses to form the so- 
called entoglossal bone (Fig. 259, 2), posteriorly to which lies the true body of the 
hyoid. The second arch, however, is well developed, and gives rise to the coruna 
(4,5), which are formed of two large pieces, which generally curve backwards behind 
the skull, without being directly connected with it. Behind the copula there is the 
remnant of a second one, which forms the hyoid process (3).” (Elements of Comp. 
-Anat., Lond., 1878, p. 472.) In the description of the hyoid in this paper the cerato- 
hyals correspond to the entoglossal bone, as referred to in the above quotation from 
Gegenbaur, and the copula of that author to the basi-hyal, his hyoid process being 
the urohyal. 
