668 GEOLOGICAL SURVEY OF THE TERRITORIES. | 
ity is marked above by quite an extensive surface for one of the nasals, 
and below by another, against which the head of the ethmoid abuts. 
The concave surface below this process and the remaining hinder moiety 
form the vault of the orbit. Another scale-like projection is thrown 
out posteriorly, deeply concave within, correspondingly convex without, 
to shield the prosencephalic lobes—the bones being joined. Huxley 
terms the pleurapophysis of the hemal arch of this segment the “ quad- 
rate”—the “‘os quadratum” of the older anatomists. Owen defined it 
as the tympanic,! it being the homologue of a bone of the vertebral skull 
generally—it was the os carré, in birds, in the writings of the eminent 
Cuvier. The tympanic bones here, as in all sauropsida, are free ossicles, 
connecting the articular ends of the lower jaw with the skull. They are 
in the Tetraonide, symmetrical and well proportioned, not exhibiting any 
marked peculiarities or deviations from a common type. The mastoidal 
and orbital arms are about of a length and calibre, the first being rather 
the larger, and is surmounted by a hemispherical articulating head for 
the cup on the lower border of the mastoid. The neck below the pro- 
cesses is moderately constricted before it expands to become the “‘man- 
dibular” end, that has beneath its tranverse elliptical facet outwardly 
the intervening notch, and then the inner and smaller one, all for artic- 
ulation with the mandible. The bone has likewise a surface to articu- 
late with the pterygoid below the orbital process, and is always pneu- 
matic. From the outer aspect of the mandibular extremity it sup- 
ports its two appendages, the bony styles, termed ‘‘squamosal” and 
malar—the first by a diminutive ball-and-socket joint articulated in 
the usual manner. The malar, as we know, is the mid-style of the 
infraorbital bar—the maxillary completing the connection anteriorly, 
and although upon superficial inspection of this striking ornithic feature 
of the lateral aspect of the skull, it seems to be firmly united in its schin- 
dylesial articulation, it simply requires ordinary maceration in the adult 
of any of the Grouse or Quails to have the three styles separate from 
each other and from their tympanic and intermaxillary connections. 
The lower jaws of the Tetraonine are singularly alike in all their: 
characteristics throughout the sub-family. The single bone is devel- 
oped in the usual way by confluency of the “articular,” “surangular,” 
“angular,” and “‘splenial” elements posteriorly, and the outer moiety by 
the “dentary” element, the hemal spine. (Plate V. See explanation 
of plates for the above-described bones.) 
The mandible in the adult has a gentle and increasing curvature 
downwards from the interangular vacuity forwards. The curvatures 
‘ ! 
1There can scarcely be a reasonable doubt left in the minds of comparative anato- 
mists that the question is now settled and the fact generally accepted that the bone 
termed tympanic and so used by Professor Owen in his writings, is the representative 
of the malleus of the mammalisa. It is the ‘‘quadrate bone” of all modern writers, 
I believe without exception, and articulates with the skull, the quadrato-jugal and the 
pterygoid and the lower jaw on either side. Professor Huxley alludes to its develop- 
ment in the following words: ‘‘In the sauropsidan embryo a rod of cartilage occupies 
the first viseral arch on each side and meets its fellow in the middle line. The rod 
becomes jointed, and the part on the distal side of the joint is converted into Meckel’s 
cartilage, while that on the proximal side of the joint is modeled into the rudiment 
of the quadrate bone, which is invariably in its earliest state cartilaginous. Soon, 
however, the quadrate cartilage ossifies, and a centre of ossification appears in that 
part of Meckel’s cartilage which articulates with the quadratum. This gives rise to 
the articular element of the mandible. All the other constituents of the lower jaw 
are developed in the fibrous tissue which surrounds the rest of Meckel’s cartilage, 
_ which structure either persists throughout life or disappears.” (On the Representatives 
of the Malleus and the Incus of the Mammalian and other Vertebrata, Proc. Zool. Soc. | 
Lond., 1869, page 401.) 
