600 GEOLOGICAL SURVEY OF THE TERRITORIES. 
acetabulum intended for it at the side of the united basi- and uro hyals, 
and most probably at the junction of the two latter bones. These two 
elements are long bones having a cylindrical shaft, terminating at either 
end in an articulating head. They arethe longest bones in the hyoid arch, 
and havea gentlecurvature upwards throughout theirextent. Their inner 
heads form an arthrodial joint on either side with the outer heads of 
the cerato-branchial elements of the thyro-hyals. These, the last bones 
of the arch, are joined in the manner already shown above. Theirinner 
ends are quite pointed, even as far as the bone goes, the extreme points 
being finished off with cartilage. They curve upwards from about their 
middle thirds, and, like the first elements of the thyro-hyals, they are 
long bones, but with curved cylindrical shafts, the outer end, however, 
being the only true articulating one. 
The lower mandible—(Pls. I and II, Fig. 3).—That portion of the bone 
which originally was separate as the dentary element, and as far back as 
to include the interangular vacuity, is firm and compact, while the re- 
mainder has much the same character as the bones of the cranium, being 
cellular and light, having only a very thin outside layer of the harder 
tissue. All of the primary segments are firmly knitted together, the only 
sutural trace to mark the margins of any one of them being the posterior 
border of the dentary elements as they bound the fenestra before and 
slope away beneath it. The articular extremities are some little distance 
below the upper outline of the bone. Their superior surfaces are in- 
dented so as to accurately receive the condyles of the tympanics on 
either side, forming the joint that allows the opening angl closing of the 
mandibles. Their under surfaces are smooth and rounded, having a 
fine ridge running across them transversely. Internally they are drawn 
out gradually into subceylindrical processes that point upwards, in- 
wards, and a little forwards, exhibiting superiorly on each, about the 
middle, an oval pneumatic foramen. ‘The upper edge rises rather ab- 
ruptly from the articular ends, presenting as it arrives near the general 
levela rudimentary coronoid for the insertion of the tendon of the tem- 
poral. With the exception of a little elevation where the dentary ele- 
ment meets the surangular, the superior outline is unbroken; it falls 
away rapidly as it approaches the symphysis, where, with the opposite 
border, it completes a little notch at the extremity. The tomium is 
not as Sharp as in the upper bill, and the mandibles do not fit nicely to 
each other until covered with their horny sheaths. The inferior border 
is rounded throughout its extent, and on a level at its posterior com- 
mencement with the under surfaces of the articular ends and running 
nearly parallel with the superior. The curve described by the rami 
before they meet at the symphysis inferiorly approaches the parabolain 
outline. ‘The sides of the jaw are nearly smooth internally and exter- © 
nally. The vacuity that occurs in so many birds at the junction of the 
middie and inner thirds is rather large, long, and spindle-shaped, and 
filled in, in the fresh state, by an attenuated membrane. 
Professor Huxley, in his Classification of Birds (Proce. Zool. Soe. 
Lond., 1867, p. 462, 5 Atomorphe), presents us with some of the most 
important cranial characters of the Strigide; and we find through the 
literature of the subject not a few authors who have touched upon the 
osteology ot this interesting group of birds. The attention of ornitholo- 
gists and others has been directed on several occasions to the asym- 
metry occurring in the skull of certain species of Owls, notably in Nyc- 
tale. In 1870, Dr. T. H. Streets, of the United States Navy, noticed 
this point and published his observations. (Proc. Acad. Nat. Sci. Phil., 
1870, p. 28.) In the next year, Robert Collett, esq., of Norway, noted 
