DE. J. CLELAND ON THE VARIATIONS OE THE HUMAN SKULL. 
169 
the Tartar and Negritic skulls described by Professor Huxley ; and has taken as an 
expression of the cerebral curvature the angle between a line laid along the anterior 
lobe of the brain in the groove formed by the roof of the orbit, and another extending 
from the torcular Herophili to the most depending part of the middle lobe. The results 
are : — 
Dean Swift . 
. . 164 
Australian 
. . 164 
Tartar . 
. . 155 
Negritic skull 
. . 156 
Gorilla . . 
. . 130 
In the lower Mammalia the direction of the orbit is so variable that it was found 
necessary to try still another method of comparison. The following results are obtained 
from vertical sections by measuring the angle between the middle line of the upper surface 
of the presphenoid in front of the optic commissure, and a line drawn so as to express as 
nearly as possible the direction of the tentorium. 
German, No. 29 
. 184 
Negro, 63 . 
O 
. 175 
Cat 
. 133 
Scotch Female, 43 . 
. 182 
Kafir, 70 . . 
. 191 
Dog . 
. 150 
Greek, 44 ... 
. 186 
Australian, 73 
. 193 
Pig . . 
. 150 
Irish Male, 53 . 
. 196 
Synostotic, 89 . 
. 175 
Deer . 
. 131 
„ „ 54 . . 
. 182 
Chimpanzee . 
. 172 
Rabbit 
. 116 
,, Female, 55 . 
. 177 
Orang . 
. 16S 
Squirrel . 
. 99 
„ „ 56 . 
. 182 
Turkey . 
. 103 
It is noticeable that this angle varies much in different human skulls, and not accord- 
ing to the variation of the angle of cranial curvature made use of in the former part of 
this paper. This is probably due partly to the impossibility of estimating the angle 
with perfect precision, partly to different arrangement of the cerebellum in different 
skulls, and partly to a circumstance seen best in the Australian, Kafir, and Negro. In 
those skulls, while the upper surface of the presphenoid is directed to a marked degree 
downwards as well as forwards, the cribriform plate of the ethmoid is directed again 
upwards and forwards, so that a mean between the directions of the two parts would 
most justly express the direction of the floor of the anterior cranial fossa in the middle 
line. The angle under consideration scarcely exceeds in some human brains the size 
found in the Chimpanzee and Orang, but in these animals the ethmoid is considerably 
turned up. Taking this into consideration, together with the comparison of the casts of 
the interior of the cranium in the human subject and the Gorilla, it may be held that 
the advance in form of the human brain as compared with the brains of the higher Apes 
consists partly in an increase of cerebral curvature, dependent on depression of the sphenoid 
and ethmoid, and on descent of the orbital roofs towards the level of the ethmoid, but to 
a greater degree consists in increased expansion both in height and breadth of the cranial 
dilatation of the cerebro-spinal canal. 
