BastiaN; on the so-called Pacchionian Bodies. 89 
as a very common locality in which these growths ma.y be 
seen, when the sinus is slit open. The bodies projecting in 
this situation push before them the lining membrane of the 
sinus, instead of perforating it, and this was the covering 
probably alluded to by Pacchionius when he spoke of the 
assumed glands in the sinus as, propria et tenuissima 
membrana, veluti in saculo conclusse.^^ Concerning them in 
this situation also Dr. Todd wrote : — It has been supposed 
that these bodies are natural structures, destined to perform a 
mechanical office somewhat on the principle of a ball valve, 
but they are frequently absent altogether, and when present 
they have no constant relation to the venosus orifices/'' Accord- 
ing to Cruvelhier,^ Haller has found growths of this kind at 
the anterior extremity of the straight sinus, whilst he himself 
once met with ^' une petite masse pediculee of a similar 
nature in the horizontal portion of the lateral sinus. I have 
occasionally found them pretty plentiful in this latter situation. 
In most cases where the Pacchionian bodies exist in any 
quantity it is found somewhat difficult to reflect the dura 
mater,, on account of the adhesions between it and the 
arachnoid on each side of the median fissure, without tearing 
away portions of the latter with the upper membrane. Where 
this occurs, when the under surface of this reflected dura 
mater is examined, there is no difficulty in detecting the torn 
portions of arachnoid adherent to it, and if the edge of one 
of such portions be held with a forceps, and carefully pulled, 
it will be readily seen as the two membranes separate, that 
the adhesion is entirely due to an interlocking, by means of 
the Pacchionian bodies, which (still springing from the cere- 
bral arachnoid) have pressed against the inner layer of the 
dura mater, destroyed its epithelial lining, and insinuated 
themselves into its substance by separating the interlacing 
fibrous bundles of which it is composed. Instead of its ordi- 
nary smooth appearance, also, the under surface of the dura 
mater in these parts will be found to have an open reticulated 
or cribriform aspect, owing to the separation of its fibres by 
the growths just dislodged from between them. After lodg- 
ing themselves in the substance of the dura mater, these 
growths still increase in size, and are developed into the 
little pear-shaped bodies, which can then only be pulled 
backwards through its meshes by exerting a considerable 
amount of traction. Some few of these bodies which have 
thus lodged themselves take on a further increase of growth, 
and soon exceed in dimensions any of those to be found un- 
attached on the surface of the arachnoid. When the skull 
* Loc. cit., t. iv, p. 537. 
