994 
Journal of Agricultural Research 
Vol. XXVIII, No. 10 
In considering the variation of the skull with age, the anterior ring, chiefly the 
frontals, of the cranium is “dead center,” from which there is development 
anteriorly and posteriorly. For the purpose of following this general develop¬ 
ment of the skull with age, there have been selected from the series of females 
the largest adult, a medium subadult, and the smallest juvenile. The general 
conclusions reached therefrom have been checked with the remainder of the series, 
but details regarding only these three will be presented in order to avoid a need¬ 
less amount of tedious statistical matter. Females were selected in preference 
to males, because their characters 
are in most respects more uniform 
and less extreme. 
Skulls of juveniles are, of course, 
much weaker than are those of 
adults. All surfaces are rounded 
and the processes are more obscure 
and poorly defined. This is a natu¬ 
ral correlation with the weaker, un¬ 
developed condition of the muscle 
system. In addition, the antero¬ 
posterior dimension of the skulls of 
juveniles have the superficial ap¬ 
pearance of stubbiness, with rela¬ 
tively much shorter rostrum and * 
diastema, crowded condition of the 
pterygoid region, and smaller bul¬ 
lae; in transverse dimensions, wider 
interorbital, narrower zygomatic 
spread, and wider braincase. A 
critical study of these points shows 
that some of the differences enu¬ 
merated above are merely optical il¬ 
lusions brought about by the lack of 
strength and ridging and the weak 
processes of the juvenile skull. In 
reality, the skulls of the two ex¬ 
tremes in age are remarkably and 
surprisingly similar in relative meas¬ 
urements, as shown both by the fig¬ 
ures and camera-lucida studies. In 
proportion of nasals to condylo-basi- 
lar length the three skulls of the 
ages selected indicate that the greatest difference between them is less than 2 
per cent; condylo-zygomatic to condylo-basilar, 1.6 per cent; nasals to condylo- 
zygomatic, 2.7 per cent. The difference in the proportion of the zygomatic 
width to condylo-basilar length is but 0.6 per cent. 
The capacity of the braincases in the whole series of males was investigated 
by filling them with No. 10 shot (see Table I, p. 981). The results are perhaps 
not so accurate as would be the case had mercury been employed, but the diffi¬ 
culty of stopping up all the vacuities and foramina of the cranium rendered the 
use of this metal impractical. The shot, however, proved satisfactory, and tests 
have shown that the normal error is only from 1 to 2 per cent. The average 
capacity of the braincase in the eight normal, adult males with greatest condylo- 
Fio. 9.—Diagrammatic ventral aspect of adult skull, 
a, Incisive foramen; b, zygomatic process of maxilla; 
c, palatal; d, palatal pit; e, squamosal; f, presphenoid; 
g, alisphenoid; h, external pterygoid plate; i, pterygoid 
plate; j, hamular process; It, audital bulla; l, mastoid; 
m, condyle; n, premaxilla; o, maxilla; p, anterior angle 
of xygoma; q, jugal; r, interpterygoid fossa; s, glenoid 
fossa; t t pterygoid fossa; u, basisphenoid; v, external 
auditory meatus; w, basioccipital; z f paroccipital 
process. 
