696 GEOLOGICAL SURVEY OF THE TERRITORIES. 
The proximal extremity of tibia in the young chick of Centrocercus has 
advanced so little towards assuming any of the definite characteristics 
of the full-grown bird, that, almost in self-defense, we take up for exam- 
ination the bone from a skeleton of a bird of the same species several 
weeks older; here we discover the superior general condylar surface 
still capped with cartilage, and the borders confining it, as yet, but 
feebly produced. The most interesting point, by far, is the appearance 
of an unusually large epiphysis, if it may be so termed, fashioned to 
and resting upon the future location of the “‘rotular crest.” 
Why this bone should be here added we cannot, as far as our knowl- 
edge extends, exactly comprehend, for in the old and mature birds of 
any of the Grouse the epi-cnemial crest is never very prominently pro- 
duced, nor is it in any of their near kin. As age advances this seg- 
ment becomes thoroughly confluent with the tibia, and leaves no trace 
of its early existence. 
The head of the bone in the adult Sage Cock is a very substantial 
affair, with pro- and ecto-cnemial ridges, well produced, that soon merge 
into the shaft; the latter ridge is usually dilated on its anterior as- 
pect, and the rather extensive concavity between them is directly con- 
tinuous with the shaft below. 
The tibia never becomes pneumatic either in the Grouse or Quails, 
and in the former, sections of its shaft are universally transversely 
oval; the fibular ridge of the upper and outer third of this portion of 
the bone in Centrocercus is about 2 centimetres long, and appears to be 
little more than a raised and roughened line. Below the fibular ridge 
we find the nutrient foramen, but otherwise the tibial shaft is very 
straight and almost entirely devoid of any markings, at least to that point 
anteriorly, where the ascending groove coming from between the con- 
dyles impresses it, and that, with an increasing intensity to its termi- 
nation over the intercondyloid notch; at this point a bony bridge is 
thrown across obliquely, the outer abutment of which is the lower. (Plate 
IX, Fig. 69.) 
The most engaging points of interest, so far as the tibia is concerned, 
center about the distal extremity of the bone. After careful examina- 
tions of the recently-killed subjects, dried skeletons, and carmine-stained 
specimens, the following result seemed to be presented with greater or 
less distinctness in every case, and these results correspond very nearly 
with Professor Morse’s invaluable investigations and studies: In the 
young of Centrocercus, several days after leaving the nest, we observe 
at the future site of the tibial condyles, encased in. the then articular 
cartilage, on either side, a free reniform ossicle. These ossify to the 
Surface in time, and the outer becomes the jibulare, the inner the tibiale ; 
both are tarsal bones. It will take time and further research to decide 
definitely as to which is the os calcis, and which the astragalus. Above 
the former, and a little towards a mid-shaft position, there is yet another — 
free ossicle; it is the intermedium of Morse. That it is another tarsal 
bone, there can be no doubt, we believe, at this date; but before we 
decide upon its special homology we must satisfy ourselves by further 
research and dissection of the young at various stages of development 
in birds and other vertebrates where this bone constitutes a feature of 
the skeleton. 
It soon fuses with the tibiale, and the latter with the jfibulare, so that 
the faintest traces are alone discernible in the bird at two months of 
age. (Plate IX, Fig. 67, KE’). At this period the subsequent bony span 
for tendinous confinement above them has not commenced to ossify. 
In the adult the apex of the intermedium aftords attachment to the 
