1008 
Journal of Agricultural Research 
Vol. XXVIII, No. 10 
to within a couple of millimeters of the posterior angle of the zygoma. There 
is great variation in the supero-inferior aspect of the portion of the maxilla imme¬ 
diately anterior to the jugal. In some (as the largest male) this detail is shallow, 
while in others (as female No. 3845) it is nearly 50 per cent deeper (see fig. 16), 
due to the formation of a sharp sort of superior crest. This extreme develop¬ 
ment is not necessarily present in the most angular skulls, but may develop 
independently, and is probably in response to certain special stimulation by 
the deep part of the masseter major muscle, and possibly by the masse ter zygo- 
matica as well. The superior border of the root, differing in thickness, is amen¬ 
able to similar influences by different portions of the masseter. 
The anteorbital foramina are about three times as high as wide; but this 
means little, as it is impossible to measure them with accuracy. They do not 
vary appreciably except in the antero-posterior extent of the adjoining fossae 
upon the rostrum. Such differences are dependent upon the development of 
the anteorbital slip of the deep part of the masseter major. Width of ros¬ 
trum is usually measured across the prominences anterior to the anteorbital 
fossae, but these are often fragile and easily injured, and it is an unreliable measure¬ 
ment on which to place dependence. 
The shape of the incisive foramina is usually constant in the present series. 
These are not wide, and there is gradual and moderate, though definite, constric¬ 
tion posteriorly. In the case of normal adults and subadults, the length of the 
incisive foramina for males averages 5.5 mm., with extremes of 5.8 and 5, a 
difference of 0.8 mm., or 14.5 per cent of the average. Females average 5.35 
mm., with extremes of 5.7 and 5, a difference of 0.7 mm., or 13 per cent. These 
foramina may be proportionately a trifle shorter and are situated relatively far¬ 
ther forward in juveniles, but after sexual maturity has been attained they vary 
hardly at all in comparison with the size of the entire skull. There are some 
examples in which the length of the foramina varies individually to some extent, 
but on the whole this measurement is quite uniform and dependable. 
Premaxillae. —Each of these bones articulates with the nasal, frontal, and 
maxilla. The ascending branch of the premaxilla projects posteriorly between 
the nasal and maxilla to join the frontal, and the resulting suture is somewhat 
variable, but not nearly to the extent that is sometimes to be found in other 
species. These branches are always pointed at the medial tips and differ negli¬ 
gibly in shape. Variation in the position of the posterior terminations with 
reference to the posterior terminations of the nasals is considerable, however. 
In 48 examples the ascending branches extend slightly farther backward while 
in 16 these may be considered as ending even with the nasals. It may or may 
not be fortuitous that among the latter large females are especially prevalent. 
Nasals. —The nasals are quite variable, probably not from any inherent 
tendency to vary, but rather because of differences in the stresses brought to 
bear by surrounding bones. They articulate laterally with the premaxillae and 
posteriorly with the frontals. The measurement of length of nasals must be 
taken with extreme care in order to prove reliable. Not only is it sometimes 
difficult to decide upon the exact posterior terminations, but the anterior tips are 
exceedingly subject to injury. There is considerable individual variation in 
length of nasals and also much difference with age, these bones often being rela¬ 
tively shorter (and wider) in juveniles. In males the normal average of this 
measurement is 7.7 mm., with extremes of 8.8 and 6.9, a difference of 1.9 mm., 
or 24.7 per cent of the average. For females the average is 7.5 mm., with extremes 
of 8.3 and 6.9, a difference of 1.4 mm., or 18.6 per cent. 
The posterior terminations of the nasals usually present a gently rounded 
aspect, although in a few they are more squarish, slightly emarginate, or so narrow 
