660 GEOLOGICAL SURVEY OF THE TERRITORIES. 
relation to each other and their development carried up to the adult 
bird. It will be observed after a glance at the writer’s drawings in 
Plate V that he has chosen the young of that grand old prairie-loving 
Grouse, Centrocercus urophasianus, as an example of the growth of the 
skull from the time above referred to in the Tetraonine. 
In this plate the first. three figures show respectively the skull of the 
young of the Sage Cock a few days after the parent has led it from the 
nest: 47 from above, 48 lateral view, with mandible, and 49 from be- 
low, the mandible removed. 
Fig. 50 shows the bird in August of the same year, and Fig. 51 the 
disarticulated skull of the same, whereas in the next plate we observe 
the skull of an old cock of the same species, that has, no doubt, trod the 
prairie for many a season. (Fig. 52.) 
In these birds the greatest amount of difference exists in point of size 
among the sexes and 
in individuals of vari- 
ous ages of the same 
\\ \ sex; so we naturally 
6a, fi \ ) find a corresponding 
: amount of difference 
\ \\ in the sizes of their 
Fig. 52 is the skull 
y of an exceptionally 
' \ large adult, ¢, chosen 
: from a bevy of sev- 
\\ \; i 
>»\\ 
32312 
crania. 
eral hundred others, 
with a view of afford- 
ing the reader the op- 
portunity of seeing 
the proportions this 
Grouse may attain, 
as far as this part of 
its skeleton is con- 
cerned. This peculi- 
arity seems to be con- 
fined to Centrocercus, and does not obtain with the other varieties, they 
seemingly arriving at maturity of growth at a much earlier period of 
their existence. Canace obscura may form an exception to these re- 
marks, but it is certain that itis not by any means so striking a char- 
acteristic in this bird. Another interesting point to be observed here, 
that no doubt has forced itself upon the reader since his inspection of 
the plates already introduced, is the unusual length of time that the 
original bony segments of this Grouse’s head retain their individuality 
over others of the class. This is indeed so, and in birds of one or two 
years of age, if we exclude the epencephalic arch of the occipital ver- 
tebra, it is not an unusual occurrence to be able to distinguish all the 
sutural boundaries among the remaining elements, and these appear to 
be persistent when applied to the nasals and the premaxillary bone of 
very old birds. We are all well aware that this rule holds good in the 
common barn-yard fowl. 
Students of the works of that eminent anatomist and observer, Owen, 
will remember that in his Comparative Anatomy and Physiology of 
Vertebrates he seems to accuse the Struthionide alone of this singular 
feature, or at least ‘those birds in which the power of flight is abro- 
gated.” Now, such of my readers as have had the opportunity of ob- 
_Bonasa winbella. 
