644 
posed in the performance of the experiment, 
oar fairly to be considered to have a share, 
and that not an inconsiderable one, in any im- 
irment of the nervous function that might 
ome apparent. The sudden removal of the 
fluid brings on fainting or even death, effects 
due to shock, and analogous to those which 
result from the sudden removal of dropsical 
fluid in particular cavities, when the organs and 
the circulation in them have become adapted 
to its pressure, as 1 cases of ascites, hydtotho- 
rax, &c. 
The interior of the arachnoid sac is moistened 
by an exhalation of a similar kind to that which 
is found in the other serous membranes. Ac- 
cumulations of fluid in the arachnoid sac, how- 
ever, are of very rare occurrence. 
Of the glandule Pacchioni—To these bo- 
dies we have already had occasion to refer in 
the description of the sinuses. We proceed 
now with a more special notice of them. 
These bodies were first formally described by 
Pacchioni, and were regarded by him as con- 
globate glands of the dura mater, from which 
lymphatics proceeded to the pia mater.* They 
have been recognized by all subsequent anato- 
mists under the name here assigned to them, 
although the idea of their physiological office 
suggested by Pacchioni has not met with ge- 
neral acceptation. Bichat suggested a more 
appropriate and scientific appellation in that of 
cerebral granulations. No anatomists have in- 
vestigated the history of these bodies so exten- 
sively as the brothers Wenzel.t+ 
The Pacchionian bodies are found principally 
along the edge of the great hemispheres of the 
brain on either side of the great longitudinal 
fissure. Here, in general, they cause the obli- 
teration of the sac of the arachnoid for a greater 
or less distance by producing adhesion between 
the visceral layer of that membrane and that 
portion of its parietal layer which adheres to 
the angle along the superior border of the falx 
cerebri. In cases where these bodies are 
numerous and well sp apt 84 it is found very 
difficult to separate the dura mater from the 
subjacent arachnoid by reason of the firmness 
of the adhesion effected by them; and when 
this adhesion exists, the corresponding surface 
of the dura mater has generally a very com- 
plicated cribriform appearance. The extent 
of surface which they occupy is very variable, 
Sometimes, but very rarely, they extend along 
the entire edge of each cerebral hemisphere; 
but generally they occupy its central for 
an extent of from one to three inches. Very 
frequently they extend outwards over the sur- 
face of the cerebral hemispheres, rarely beyond 
half an inch or an inch. The arachnoid mem-’ 
brane in their immediate vicinity is always 
opaque. 
Bodies, somewhat similar, are also found oc- 
* Ant. Pacchioni diss. epistolaris ad Luc. 
Schroeckhium de glandulis conylobatis dura: me- 
ningis humane, &c. &c. Rom, 1705, et Opuscu- 
lum Anatomicum de dura meninge, in Opera Omnia. 
Rom. 1741. a 
t+ Wenzel, de penitiori cerebri structura, Tu- 
binge, 1812. 
NERVOUS SYSTEM. (Nervous Centres. Tue Mentxces.) 
casionally on the choroid plexuses of the latera 
ventricles. Very frequently we meet with 
nulations of a like kind in the fringe-like pro= 
cess of pia mater which descends from the 
velum interpositum to surround the pines 
gland, and also upon the little processes of 
that membrane which go under the name_ 
choroid plexuses of the fourth ventricle. = 
Wherever these bodies are found, they show 
a remarkable tendency to congregate in clust 
around venous trunks. In examining the 
along the edges of the hemispheres, we ni 
that they are most numerous around the veir 
which pass from the pia mater in that situatio 
into the superior longitudinal sinus. This 
dency, probably, explains the occurrence ¢ 
these bodies in some of the sinuses. They ai 
most commonly met with in the superior long 
tudinal sinus, as already stated ; are al 
found in the lateral sinuses, and sometimes bi 
rarely in the straight sinus. In all these si 
ations these bodies appear to stand in a sir 
relation to the sinuses; they have penetrated t 
fibrous tunic of their walls, and pushed befo 
them the inner or venous tunic. i 
In point of size and shape the Pacchic 
bodies resemble minute granulations; their 
lour is white, like that of coagulable lym 
and not unlike that which is occasionally s 
upon serous surfaces after chronic infl 
tion. A granular lymph, taking son 
similar form, is occasionally seen on 
ripen membrane of the rectum after dy. 
t some the granulations 
as ssclatel Siemmrice of the a 
arachnoid membrane. At others they are 
lected in clusters round a common stem; 
when the membrane is removed and float 
water, this bothryoidal disposition may be 
displayed. A large proportion of them ¢ 
by their pressure, an adhesion between 
opposed surfaces of arachnoid membrane; 
those which are attached to a stem are 
most likely to project into the interior 
sinuses. ‘ 
When examined by a ner 
these bodies appears to consist of a mi 
minute granules enclosed in a membr 
sac; when the body is pediculated, its 
exhibits a series of strise which take the di 
of its length, and probably result from 
tudinal folds of the membrane which fot 
Dilute acetic acid causes them to sw 
gelatinifies the bodies, and sometimes ¢ 
epithelial scales upon the surface of thi 
brane which covers them. is 
The following explanation of this” 
may be offered. he primary 
granular lymph takes place among fl 
of the pia mater. e small boe 
formed push the arachnoid membrani 
oo as asac or covert in a 
the granular mass is only partially covere 
then it causes merely a slight projection 
surface of the visceral layer of arachno 
in others the mass is completely covered 
stalk is gradually formed ; and when 
granular masses have been deposited 
ately contiguous to each other, thes 
ks 
4 
