628 GEOLOGICAL SURVEY OF THE TERRITORIES. 
as already stated, there is a total absence of any such indication. If we 
remove the lower mandible from the skull in any of the Class Aves, and 
place the remainder on the horizontal plane, with the basi-cranii down- 
wards, we observe that in different skulls there exists i this position 
differences in equilibrium, and differences in, what we wiil call, the an 
terior and postcrior bearing points, or the points upon which this part 
of the skull rests upon the horizontal plane. To illustrate this in the 
skull we are studying, we find, when placed as directed above, that 
its equilibrium is quite stable, and that it rests posteriorly upon the tym- 
panics, anteriorly upon the tip of the superior mandible, which consti- 
tute, respectively, its posterior and anterior bearing points. In this 
case there is but one anterior bearing point, with two posterior ones. 
This is a very common resuit, but there are at the same time many ex- 
ceptions to it, as in Numenius, and many species of the family Anatide. 
Again, if we erect a perpendicular from one of the posterior bearing 
points, or the posterior bearing point, for sometimes it is the condyle, 
we find that the planes passing through the circumference of the fora- 
men magnum and the occipital vertebra, and the point where the foot 
of this perpendicular and the posterior bearing points coincide, make 
certain angles with the horizontal plane (the ordinary horn protractor 
is the best instrument to take these angles with), which we will call, re- 
spectively, the angle of the foramen and the angle of the base. These two 
angies, in many instances, practically coincide, as in our Lark, where 
they make an angle of 40° with the horizontal plane. In the cut, H H’ 
is the horizontal plane; a the anterior and p the posterior bearing points. 
These angles also differ in many birds; e. g., the anterior bearing 
point in Ardea herodias is the tip of the upper mandible, the posterior 
ones being the inner of the three facets.on each tympanic; the angles 
of the planes of the base and foramen about coincide, and is 50°. In 
many of the Owls and diurnal birds of prey, the bearing points being 
the same as in the last example (it being, however, the inner facet of 
two on the tympanies, as a rule), the combined angles, or either of them 
separately, is very small, or the base and foramen-may be found to lie 
nearly in a plane parallel to the plane upon which the skull rests, or the 
0° gn° 
Fa SE \ . f v 
Bie ro ee HE 
angles are 0°. We see then that in the present case, the bearing points 
being given, the angle of the combined planes is 40°, which fact, even 
without actually taking the angles in question, conveys to our minds 
about the “pitch” or relation of the basi-cranii to the other salient feat- 
ures of the skull. Taken accurately, these angles, it is obvious, would 
