90 Bastian, on the so-called Pacchionian Bodies. 
cap is removed in such cases we see slight bulgings on the 
surface of the dura mater on either side of the middle line ; 
at later stages these prominences would be more manifest, 
and at last the outer layer of the dura mater having be- 
come thinned and then eroded, portions of the growths 
protrude, dilBPering, however, in appearance from that which 
they present when smaller and seen on the surface of the 
arachnoid."^ They have now a less opaque and more pel- 
lucid aspect, and instead of being white in colour are seen 
to have a faintly reddish or even yellowish tinge. Sometimes 
several of these bodies, small in size and situated together in 
a little patch, may be seen on the surface at a slight distance 
from the middle line, the outer layer of the dura mater being 
absent over the area occupied by them. It seems a more 
probable supposition to imagine that this has been caused 
to disappear by pressure and erosion, than to account for its 
absence by a congenital defect, as some have suggested, seeing 
that this hypothesis is inadequate to explain why it should 
be that in preference growths should spring up on an inde- 
pendent subjacent membrane, precisely opposite those very 
parts where there is a deficient development in the one above 
it. Certain of the little tumours generally situated pretty close 
to the middle line, and mostly solitary in position, attain a 
morec onsiderable size still. They produce, as they increase in 
bulk, at first a mere depression in the corresponding region of 
the inner table of the skull, and at last an actual erosion of 
this, and even of the outer table, if their growth still con- 
tinues. I have several times seen the outer table of the 
skull reduced to a plate of extreme tenuity, though never 
actually perforated. Dr. Ogle,t however, has lately described 
and figured cranial bones which have been perforated by 
these bodies, and mentions also that Mr. Turner, of Edin- 
burgh, has once seen an actual perforation of the right 
parietal bone, in which the aperture in the outer table was 
large enough to give passage to an ordinary pea, whilst, as is 
frequently the case, the inner table was worn away over a 
* This difference in appearance led me at one time to imagine tliat they 
might be structures of a different nature. In fact, knowing nothing very 
definite about them, I looked upon the little growths found on the dura 
mater as Pacchionian bodies, and in earlier autopsies was in the habit of 
looking upon the opaque granulations of the araclinoid as something quite 
distinct. This^ however, I soon found to be erroneous. I now suspect that 
the opaque white appearance of the bodies seen on the surface of the arach- 
noid is partly a post-mortem effect due to the absorption of serum, since 
thos'i found on the surface of the dura mater assume the same appearance 
after a short immersion in water. 
t 'Brit, and For. llev./ Oct. 1865, pp. 502—4, figs. 21—23. 
