692 ‘GEOLOGICAL SURVEY OF THE TERRITORIES. 
to the cotyle, the anterior half of which it eventually forms. From this 
- point it arches backwards over the future ischiatic foramen. The inner 
margin of the post-acetabular portion is rather more rounded than its 
anterior extension, and directly opposite the “ring” presents for exami- 
nation the depressions of the tranverse processes of the ninth and 
tenth sacral vertebre in elongated and coneave facettes. The ninth 
vertebra seems to be the first to come in contact with the ilia, and the 
pelvis is so inclined that the remaining vertebre soon, by their outgrow- 
ing apophyses, come in contact with it, ultimately fusing to develop the 
compound bone, usually termed sacrum. A good idea may be gained 
of the form of the ischium and os pubis by an inspection of Fig. 62, 
Plate VIII, at this stage of the bird’s existence. For very obvious 
reasons the stoutest part of the ischiatic element surrounds the acetab- 
ulum ; an inferior process, extending towards a similar one directed 
backwards by the ilium, grasps the head of the os pubis between them. 
From this point the ischium sends backwards a triangular thin plate, 
rounded behind, that is intermediate in length between ilium and 
pubis. This latter is satisfied to follow suit and direction by contribut- 
ing a simple and diminutive spine. This crosses soon after the pubis 
has given its share to the cotylis, the obduratic notch of the ischium, 
converting it, as the bones fuse, into the obdurator foramen. 
We give an additional figure in the Plate, Fig. 63, that exhibits the 
further advances of these elements towards maturity. The bird is now 
nearly two months old, and it will be seen that one after another the 
vertebre impinge upon the iliac margins within. The ilia and ischia 
extend behind, including vertebra after vertebra, from a series that at 
this age might be easily taken for an extraordinary number of coccygeal 
segments. The head of the pubis at this time is entirely out of pro- 
portion with its rib-like extension, it having so spread and insinuated 
itself into the formation of the cotyloid ring as to form about one-fifth of 
its circumference. At this stage, too, the necessary cartilage begins to 
be thrown out to form the future anti-trochanter on the ilium. 
So much for pelvic development; now let us examine this bony basin 
as it is seen in the full-grown representatives of the genera. 
The manner in which the confluent sacral vertebre meet the ossa in- 
nominata forming the ilio-neural canals and sacral sutures has already 
been defined above, so that here nothing more need be said of the mid- 
section of the pelvis taken as a whole. We give among the plates fig- 
ures of the pelves of Centrocercus, Canace canadensis, Lagopus, and Cu- 
pidonia from the skeletons of the adult birds, and if the reader will 
compare the lateral views given of the Ptarmigan and the Sage Cock 
he will see how few the differences are that exist between the two birds, 
and the same may be said, we assure you, for its superior and inferior 
views; in fact in the case of Logapus it may be stated that its pelvis in 
most instances is the perfect miniature of this bone found in Centrocer- 
cus in all respects. This applies, also, though not quite as strictly, to 
Canace and Bonasa. Of course certain minor differences are easily to 
be picked out, such as a greater fullness there, as slightly deeper depres- 
sion here, and so on; still our plate of Tetrao canadensis represents the 
general pattern of the pelvis among ali the North American Grouse, save 
Pedicecetes and Cupidonia. In the superior aspect of this confluent bone 
in a fine specimen of Canace obscura, we find the pre-acetabular por- 
tions of the ilia very much depressed below the general surface of the 
bone, and quite concave. The convex anterior borders are embellished 
with a flattened rim that bounds them, often produced forwards as two 
median sharp-pointed processes. The post-acetabular surface is raised, 
