448 
Proceedings of the Royal Society 
inner end of the left parietal opening a shallow groove pro- 
ceeded, which ended in the groove for the superior longitudinal 
sinus, and had apparently, at one time, lodged a small venous sinus. 
Anteriorly, the right parietal bone sent forward into the frontal a 
beak similar to those the author. had described in some of the sca- 
phocephalic crania recorded in his former paper. Traces of a suture, 
visible only externally, might be seen commencing at the coronal 
suture, immediately to the left of the base of the beak. It ex- 
tended in an interrupted manner backward for about an inch and 
a half, and then disappeared, so that from this spot, to a point 
midway between the two parietal openings, the sagittal suture was 
entirely obliterated, and the two parietal bones were completely 
blended together. The other sutures of the skull-cap were well 
marked, both internally and externally. 
The author then discussed the probable modes of production of 
these malformations. He argued that the opening in the occipital 
bone was due to want of union in the middle line of the ossific 
spicula proceeding from the two centres of ossification from which 
the inter-parietal, or cerebral, part of the occipital bone is developed. 
The malformation might be compared, therefore, with the deficiency 
in the neural arches of the spinal column, occasioning a spina bifida. 
The two large openings in the parietal bones were of a different 
nature ; they were not congenital deficiencies in the middle line ; 
they did not occur along the line of junction of spicula — proceeding 
from ossific centres orginally distinct, but were placed laterally, 
•and each was situated between the eminence which seemed to be 
the centre of ossification for the parietal bone in which it occurred, 
and the middle line. The openings, indeed, occupied the position of 
the parietal foramina, but were many times larger than those aper- 
tures are in a normal skull. The possibility of these being greatly 
exaggerated vascular foramina was then discussed, the cribriform 
condition of the membrane closing them over, and the relations of 
the grooves for the venous sinuses internally, seemed to favour such 
a conclusion. Abnormalities in the construction of the bones of 
the skull-cap, i.e. of the bones developed in membrane, are appa- 
rently more frequent than those of the basis cranii, which are de- 
veloped in cartilage. This is probably due to the circumstance, 
that the areas of the different bones are less precisely defined, and 
