92 BastiaNj on the so-called Pacchionian Bodies, 
The description here given of the Pacchionian bodies 
differs to a certain extent from that advanced by Luschka> 
whose views also seem to have been received by Wedl"^ and 
Eorster^t since^ according to him^ all the most important 
of these growths^ pathologically speaking, namely, those 
which insinuate themselves into the dura mater, appear on 
its external surface,, or project into the longitudinal sinus^ 
take origin from parietal arachnoid. But quite indepen- 
dently of the fact, that the only representative of this mem- 
brane now believed to exist by Kolliker and other leading 
histologists is a layer of epithelium, J I have fully satisfied 
myself, after the most careful examination, that so far as can 
be ascertained, all these growths which imbed themselves in 
the dura mater or project into the sinuses, as well as those 
which remain free^, seem to spring from the cerebral arach- 
noid. § This is an arrangement easily demonstrated when, as 
is so often the case, portions of arachnoid corresponding to 
growths imbedded in the dura mater are found adherent to 
the under surface of this membrane, having been torn off 
during its reflection, since, on pulling the two membranes 
asunder, as before stated^ many of the growths still firmly 
attached to this fragment of the visceral arachnoid^ emerge 
uninjured from between the fibres of the dura mater, whilst 
the more slender pedicles of others are ruptured. The same 
thing, of course, occurs in the original turning back of the 
dura mater — certain of the pedicles give way, instead of the 
ararchnoid in all cases tearing, in order to permit of the 
separation of the adherent membranes. In such cases, where 
rupture has taken place, whether the Pacchionian body be 
situated in one of the sinuses or on the surface of the dura 
mater, if we pass the point of a fine needle through the mem- 
brane as nearly as possible in the direction of its pedicle, we 
shall always find it emerge on its under surface at a point 
where the fibres of the dura mater have the characteristic open 
cribriform arrangement, and in most cases be able to discover 
the broken extremity of the fleshy-looking little pedicle. 
Continuous as these bodies are with the arachnoid, so are 
their histological elements precisely the same. I have not 
been more successful than other observers in recognising 
* 'Rudiments of Path. Histol.' (Sjd. Soc), 1855, p. 350. 
t 'Lehrbuch der Patliolog. Anatom.' 
X See coueluding note. 
I Virchow and many of the other German anatomists have now almost 
ceased to use the word arachnoid at all, believing that no distinct membrane 
exists to which this name can be applied. They regard the so-called 
'parietal arachnoid' simply as the epithelial lining of the dura mater, and 
the * visceral ' layer as only the condensed superficial layer of the pia mater. 
