46 BULLETIN OF THE LIVERPOOL MUSEUMS. 
examined, we have found the foramina present in 66 per cent., absent in 33 
per cent., and present as a single median hole in 1 per cent. 
At the same time it is difficult to understand how even a considerable 
vascular disturbance, such as a blood island or a circulus venosus, much less 
a mere emissary vein or meningeal artery, could account for perforations of 
the size of those recorded. 
With the object of ascertaining if the arrangement of the diploic veins in 
normal crania would throw any lght on the conditions, we have filed off the 
outer table of the skull from five crania. In the cases examined the arrange- 
ment was fairly regular throughout. A large posterior temporal vein collects 
from the upper part of the parietal bone, and communicates in some cases 
with the occipital vein. In one case a “ circulus venosus ” was present (but 
not in the position of the perforations), but the bone was as well ossified 
within the circle as elsewhere. 
Ossification of the Parietal Bones—The examination of ossifying parietal 
bones throws some light upon the formation of foramina, depressions, and 
perforations. In all our specimens of fcetal parietal bones, there was only 
one example of apparent ossification from more than one centre. In a three 
months’ embryo the bone formation is occurring in two separate areas which 
are joined together, however, along a line which passes vertically down the 
centre of the bone. The examination of eighty-five. parietal bones in nine 
months’ foetuses shows the existence of a very constant cleft in the upper 
border of the bone, in the position of the parietal foramen, formed by a 
vessel which produces a rounded or oval notch (Fig. 10) at the outer angle of 
the cleft. This cleft is present in seventy specimens. In fifteen cases it is 
absent or indistinguishable from the numerous small serrations along the 
upper border of the bone. 
The presence of this emissary vessel is thus able to retard the bone for- 
mation in the situation of the parietal foramen. In six cases out of the 
eighty-five, there were remarkable thinnings, even (in two cases) perforations 
in the parietal bones, placed symmetrically in one or more situations (Figs. 
9, 10, 11). When present, these perforations are oval in form, are due to 

Fries. 9, 10.—Partetat Bone or Two Nixe-MontH Faruses 
PERFORATED AND THINNED. 

