DE. J. CLELAND ON TELE VARIATIONS OE TELE HUMAN SKULL. 
129 
A perceptible difference exists in respect of cranial curve between the skulls of dif- 
ferent nations, and this difference displays a distinct relation between the amount of 
curve and the length of base-line. Taking males only into account, the greatest cranial 
curve is found in the German skulls, in which the average amounts to 187°, and next to 
them come the Irish; while in the Kafirs the average is lowest, amounting to 169°; and 
next them come the Esquimaux and Negro. Thus the German and Irish skulls, which 
have the base-line short, are highly curved, while the Kafir and Negro skulls, which have 
the base-line long, are less curved. So also, excepting in the case of the Germans, the 
average curve of the female skulls is greater than the curve of the males of the nation 
to which they belong. These differences recall to mind Virchow’s theory of kyphosis in 
the skulls of Cretins, according to which, in cases of premature synostosis of the base, 
increased curvature supplies a means of enlargement of the cranial cavity, which to some 
extent compensates for the arrested basal growth. Without venturing to agree with 
that theory in its details, as an explanation of the pathological form of the skull in 
Cretins, to which further reference will be made, it may be allowed to allude to it as 
the first recognition of the principle that increased curving of the base of the human 
skull is a means by which the cranial cavity may be enlarged*. In the estimate, how- 
ever, of the cranial curve now being made there is included an important element not 
taken into account in Virchow’s angula sell® (sattelwinkel) or any modification of it, 
viz. the foramino-basilar angle, which indicates the degree in which the commencement 
of the inferior wall of the cranial cylinder is bent forwards from the spinal inlet ; and 
since, as has been seen, this angle compensates and to a great extent varies with the 
curve estimated in this paper by the orbito-basilar angle, and which Virchow estimated 
by means of his angula selke, it is quite evident that the increase of cranial curve now 
spoken of as a means of expansion of the cranial cavity is entirely different in detail 
from Virchow’s kyphosis. The size of the foramino-basilar and orbito-basilar angles 
individually varies according to a totally different law from that which regulates the 
cranial curve ; and seeing that accordingly as the foramino-basilar angle is large or 
small, so also to a certain degree is the orbito-basilar, the base of a skull may be termed 
level when both angles are large, and steep when both are small. 
The base of the skull at birth is more level than afterwards, and it is still more level 
before birth. In the foetus of the fourth month, in consequence of the want of develop- 
ment of the arch as compared with the base, a remarkable steepness or want of opening 
of the foramino-basilar angle is combined, contrary to the rule in the adult, with a very 
large orbito-basilar angle. In all the other skulls of foetuses and infants examined the 
orbito-basilar angle is above the adult average, and in most of them the foramino-basilar 
angle is likewise large, although in the eight months’ foetal skull 6 and the infant 
~ It will appear in the sequel that diminished curving of the base may likewise become a means of enlarging 
the cranial cavity. Increased curving is only a means by which the base accommodates itself to the growth of 
the roof-bones when its own growth is limited ; but if the arch and base be each of a given length tho cranial 
capacity will be increased by diminishing the curve of the base. 
