640 
pia mater exists in connexion with brain or 
spinal cord, whether on the surface of these 
organs, or in the ventricles of the former. It 
serves to fill up various inequalities in the cra- 
nial or spinal walls, and it accumulates in 
greatest quantity in those situations where the 
sub-arachnoid space affords the greatest ca- 
pacity. 
Majendie describes four situations at which 
this fluid accumulates in greater quantity than 
at other places on the surface of the brain.. The 
most considerable of these, which he desig- 
nates the posterior conflux, is situated below 
and behind the cerebellum; it corresponds to 
the posterior surface of the medulla oblongata, 
and is covered behind by the layer of arachnoid 
which extends between the medulla and the cere- 
bellum. (Vid.supr. p.638.) It is here that, ac- 
cording to Majendie, a communication takes 
lace between the fluid on the exterior and that 
in the ventricles, at a point corresponding to 
the inferior extremity of the fourth ventricle. A 
second, or inferior conflur is found immedi- 
ately in front of the pons Varolii; it is situated 
between the crura cerebri, and contains the 
basilar artery. It is, in fact, only the posterior 
part of what Majendie designates the anterior 
conflux, which extends forwards to the com- 
missure of the optic nerves, pees i Aa the 
central depression between the middle lobes 
of opposite sides, and bathing in its fluid the 
commissure, the tuber cinereum, the infundi- 
bulum, and the trunks of the anterior cerebral 
arteries. It communicates with the posterior 
fissure beneath the crura cerebelli. € posi- 
tion and the extent of this conflux is indicated 
by the separation of the visceral layer of the 
arachnoid membrane over the central part of 
the base of the brain. Doubtless the accumu- 
lation of fluid around so many parts of impor- 
tant function and delicate structure, is a va- 
luable safeguard to them against the communi- 
cation of shocks from the walls of the cra- 
nium. A fourth conflux is called superior ; it 
is situated behind and a little below the level of 
the corpus callosum, behind the pineal gland, 
and above the tubercula quadrigemina. It 
communicates around the crura cerebri with the 
anterior conflux, and with the posterior conflux 
by the fissures which separate the superior ver- 
miform process from the hemispheres of the 
cerebellum. The fluid contained in it bathes 
the pineal gland, the tubercula quadrigemina, 
the superior vermiform process, and the vene 
Galeni as they empty themselves into the strait 
sinus. 
As the fluid is in contact with pia mater, 
it is plain that it must surround and support 
the roots of all the nerves which proceed from 
both the brain and spinal cord, and that all 
the bloodvessels which penetrate or emerge 
from those organs, or which ramify in the 
pia mater, must also be bathed by it. The 
fluid surrounds the nerves as they emerge from 
the cranium or spine, and maintains contact 
between the layers of arachnoid membrane 
which compose the sheaths that accompany 
them in their outwards. Majendie 
states that this aid ‘covvenpatiies the roots of 
NERVOUS CENTRES. (Human Anatomy. Tut Mewrnces.) 
the fifth pair of nerves as far as the Gasserian 
ganglion, and that it bathes and mingles with 
the fibres of the ganglion itself, as well as of 
the three nerves which originate from it. : 
however, I think extremely doubtful. . 
That fluid exists in the ventricles of # 
brain has long been known to anatomists; an 
it seems highly probable that this fluid is s 
creted by the of pia mater which 
found in all i caviticn te ibly by dl 
membrane which lines their vihing 
internal fluid communicate with that in 
sub-arachnoid space? Majendie affirms that 
communication takes place by means of an opt 
ing which is situated at the inferior extremity 
the fourth ventricle. I have not been q 
satisfy myself of the existence of such an a 
ing; the following is Majendie’s description 
it: “ The true orifice, constant and normal, | 
which the cerebro-spinal fluid contin 
either to enter the ventricles or 
issue from them, may be seen at the infer 
termination of the fourth ventricle, at the p 
named ‘ le bec de la plume’ by the old ana 
mists. 
“ To demonstrate the existence of this o 
fice it is necessary to raise up, and to sep 
slightly from one another, the lobules of t 
inferior vermiform process of the cerebellu 
and without breaking any of the vascular | 
lesions which unite this part of the cerebell 
with the spinal pia mater, we ive 
angular excavation which terminates the fe 
ventricle. Its surface is smooth, even (px 
and is prolonged as far as the ventricle of 
cerebellum. Such is the anterior part of 
orifice : the lateral and superior parts are for 
by the choroid plexuses of the n and 
horny medullary lamella (valve of Tarin), 
extent of which is variable, and which adh 
to the prominent border of the fourth 
The form and dimensions of the opening 
with the individual, and with the quan 
cerebro-spinal fluid, so that when the 
exists in considerable quantity the open 
admit the extremity of a finger. Most 
quently, when the quantity of the ligt 
normal, the orifice does not exceed | 
three lines in diameter in every direction 
it is frequently subdivided by vessels 4 
= from the medulla oblongata to the ce 
um. Sometimes the orifice is icl 
one or by both of the posterior cerebell: 
ries which pass across it.” 
Such is the description of the or 
which Majendie has given the high 
title “* Orufice des cavités encephaliques 
states that when fluid is injected into the 
sub-arachnoid cavity, it makes its in 
ventricles of the brain through this or 
Statement sufficiently difficult to pre 
veilhier, who seems to Jean towards ] 
opinion, admits nevertheless several 
objections to it. The most important 
appears to me to be that the m 
oritice which is brought into view b 
thod directed by Majendie, are i 
have the appearance of neml 
And it is recorded by M. Martin St. Ange 
Pn. 
