143 
extremities, but enlarging towards the middle, where it forms 
two ridges (bourrelets), united by a linear continuation, which 
is slightly depressed in the middle.” 
“Below the left ridge the bone exhibits an obliquely inclined 
surface, six lines (French) long, and twelve lines wide.’ 
This last must be the surface, the contour of which is shown 
in Fig. 25 a, below 6. It is particularly interesting, as it sug- 
gests that, notwithstanding the flattened condition of the 
occiput, the posterior cerebral lobes must have projected con- 
siderably beyond the cerebellum, and as it constitutes one 
among several points of similarity between the Neanderthal 
cranium and certain Australian skulls. 
Such are the two best known forms of human cranium, 
which have been found in what may be fairly termed a fossil 
state. Can either be shown to fill up or diminish, to any 
appreciable extent, the structural interval which exists between 
Man and the man-like apes? Or, on the other hand, does 
neither depart more widely from the average structure of the 
human cranium, than normally formed skulls of men are 
known to do at the present day ? 
It is impossible to form any opinion on these questions, 
without some preliminary acquaintance with the range of 
variation exhibited by human structure in general—a subject 
which has been but imperfectly studied, while even of what is 
known, my limits will necessarily allow me to give only a 
very imperfect sketch. 
The student of anatomy is perfectly well aware that there 
is not a single organ of the human body the structure of 
which does not vary, to a greater or less extent, in different 
individuals. The skeleton varies in the proportions, and even 
to a certain extent in the connexions, of its constituent 
bones. The muscles which move the bones vary largely in 
their attachments. The varieties in the mode of distribution 
of the arteries are carefully classified, on account of the 
practical importance of a knowledge of their shiftings to the 
