Bastian, on the so-called Pacchionian Bodies. 99 
and they undergo a corresponding increase in size. Still 
their growth is slow^, and the pressure exerted upon the 
cerebrum can only be insignificant, seeing also that the direc- 
tion is outwards towards more vascular parts, causing them 
to press upon the inner table of the skull, and finally produce 
more or less deep erosions in the vault of the cranium. Here, 
indeed, is a source of danger, owing to the weakening of the 
bony case in which the brain is lodged, rendering it less able 
to resist the effects of blows or external violence of any kind. 
But the projection of these growths into the sinuses, and 
their increase in this situation, seem to be the course most 
likely to be attended with deleterious results, since, as foreign 
bodies, they may lead to a blocking up of the sinus, either 
from the deposition of fibrinous coagula upon them in certain 
states of the system, or from an actual increase in their own 
number and size. This latter effect would doubtless be of 
no very unfrequent occurrence were it not for the conserva- 
tive influence of the tough, elastic lining membrane of the 
sinus, which, in all probability, impedes the growth of these 
bodies, partly by its strength and pressure, and partly because 
it does not give a sufficiently ready passage to the flowing 
pabulum afforded by the serum of the blood, in which these 
structures are immersed, and which, could it be assimilated 
more easily by the Pacchionian bodies, might cause them to 
grow so as almost invariably to block up the sinus, and hence 
lead to the most serious results."^ 
* Since this paper was written I have seen a communication on the 
Pacchionian bodies by Ludwig Meyer (' Virch. Archiv.,' vol. xix, p. 171 
and p. 288), in which he not only insists upon the fact that these growths 
are invariably developments from the visceral arachnoid, but also has antici- 
pated me in the recognition of the completeness of their epithelial covering. 
Dr. Cleland, however, I have also found, in spite of Meyer's statements, re- 
affirms that some of these bodies do arise, in the manner described by 
Luschka, from the internal surface of the dura mater (parietal arachnoid), 
in a paper in the * Glasgow Med. Journal,' 1863, p. 148. {Note appended 
June 19, 1866.) 
