210 SOME NOTES ON THE EAELY HOMINID^E 
The chief points of interest in regard to the Piltdown 
skull are : — 
1. The brain-case is, without a doubt, human ; the vault 
of the skull, and the flat bones generally, are, however, of much 
greater thickness than in modern man. It would be interesting 
to know whether the pachyonian bodies had been evolved 
in these early men, as there can be little doubt that their 
presence is closely related to the thinning out of the cranial 
vault, which in modern man forms so marked a contrast to 
what maintains in primitive skulls. 
I have no work of reference at hand, but, if my memory is 
not cheating me, these bodies which spring from the arachnoid 
mater, or middle membranous covering of the brain, do not 
become functional until about the age of eighteen, after which 
period they continuously exert an absorbing influence on the 
inner table of the cranial vault, and thus prevent too great a 
thickening from occurring in this region. It might be offered as 
a suggestion that in modern man, where the brain is so highly 
developed, this thinning-out influence of the pachyonian 
bodies was associated with the growth of the brain, and by 
their presence prevented any encroachment of the inner table 
of the skull in the direction of that most delicate organ. 
2. The cranial capacity is about 1070 c.c., which is low, 
but is not lower than the lowest savages of to-day. 
3. The forehead is fairly developed, and there is an absence 
of the massive brow-ridges (superciliary ridges) which are so 
characteristic of some ancient skulls. 
4. The lower jaw offers some interesting points for exami- 
nation. The ascending rami are wide, and the sigmoid notch 
(which lies between the two projections surmounting the 
ramus— namely, the condyle and coronoid process) is shallow. 
5. The symphysis or junction of the two halves of the jaw 
is reinforced by a distinct plate of bone situated on the internal 
aspect, which sweeps across the angle of recession, and evidently 
adds great strength to this part of the jaw. In modern man 
this osseous bridge or ledge is absent, and it is well to note 
that it is a structure of purely simian nature. (See Eig. 9.) 
The roughness for the genio-hyoid and genio-hyoglossi 
muscles are absent ; and when this is taken in conjunction 
