NERVOUS CENTRES. (Human Anatomy. Tat Mentnces.) 
be attached in a cluster to the same stem. The 
fact that epithelial particles may be seen upon 
the surface of the membranous sac of some of 
the bodies is sufficient proof that it is derived 
from arachnoid membrane. If this be ad- 
mitted, then it seems impossible to come to 
any other conclusion than that the pia mater is 
the seat of the primary deposit, and this opi- 
nion is confirmed by the fact that we meet with 
_ the Pacchionian bodies on the internal pro- 
_ cesses of the pia mater, when we have no evi- 
_ dence of the existence of arachnoid membrane. 
Orit might be conjectured that these bodies 
indicate a degenerate condition of the elemen- 
tary particles of the superficial layer of the grey 
- matter of certain convolutions, produced by 
equent irritation. 
_ Arethe Pacchionian bodiesnatural structures? 
The great frequency with which these bodies 
‘are met with in the various situations above- 
‘meutioned, has induced many, even in the 
resent day, to regard them as normal struc- 
ures, the physiological office of which is as 
yet unknown. But there are many facts which 
Strongly militate against such a conclusion. In 
‘the first place it may be observed that Pacchi- 
onian bodies never occur in the earliest periods 
of life. In the course of a long experience in 
anatomical investigations I have never seen 
them at a period antecedent to six years. The 
others Wenzel, who made a series of special 
examinations with a view to determine this 
stion, make the following statement. In 
dren, from birth to the third year, these 
ies, if they ever occur, must be very few. 
From the seventh to the twentieth year they 
ometimes are numerous. From the latter pe- 
iod to the fortieth year their number is consi- 
ble, and the nearer we approach the fortieth 
year the greater does.it become. Lastly, from 
he fortieth to the one hundredth year these 
bodies are found in great numbers. 
_ It must be further remarked that even at 
those periods of life when the Pacchionian 
ies are found in greatest numbers, cases fre- 
‘quently occur in which no trace of them can 
be found. There is likewise the greatest variety 
as to their number and size, in different indivi- 
als of the same age. 
has always occurred to me to find them 
numerous in cases where I had reason to 
ww that the brain had been subject to fre- 
uent excitement during life. In persons ad- 
dicted to the excessive use of spirituous liquors, 
se of irritable temperament and who were 
quently a prey to violent and exciting passions, 
are almost uniformly highly developed. 
@ Pacchionian bodies are peculiar to the 
man subject. Nothing similar to them has 
n found in any of the inferior classes of 
teference, then, to the question, what is 
the nature of these bodies, I have no difficulty 
in stating my opinion that the evidence greatly 
preponderates in favour of their morbid origin ; 
that they are the product of a chronic very 
gradual irritation due to more or less frequent 
functional excitement of the brain itself. It is 
not unlikely that the friction to which the 
Opposed surfaces of the arachnoid are conti- 
645 
nually subjected in the movements of the 
brain, especially when they are of a more rapid 
and violent kind, as under states of cerebral 
excitement, may contribute to the develope- 
ment of many of the appearances connected 
with these bodies. The opaque spots which 
are of such frequent occurrence upon the sur- 
face of the heart may be quoted as an example 
of a morbid change, very commonly met with, 
and resulting probably from the friction against 
each other of opposed serous surfaces. Were 
the Pacchionian bodies normal structures, they 
would not be so frequently absent from brains 
which afforded every other indication of being 
in a healthy state; nor should we find opacity 
of the arachnoid (a decidedly unhealthy con- 
dition) so commonly coexistent with the full 
developement of them. Again, were they 
a necessary part of the healthy orgamism, we 
might expect to find them more constant as 
regards size, number, and the extent of surface 
over which they were placed. 
Of the ligamentum dentatum (serrated 
membrane of Gordon).—This structure forms 
a part of the mechanical arrangements con- 
nected with the spinal cord and the roots of its 
nerves. It is found in the subarachnoid 
space, adhering on the one hand to the pia 
mater, and, on the other, attached at certain 
intervals to the dura mater. 
The ligamentum dentatum consists of a nar- 
row longitudinal band, adhering by its inner 
straight border to the pia mater on each lateral 
surface of the spinal cord, midway between 
the anterior and posterior roots of the spinal 
nerves, reaching from the highest point in the 
cervical region down to the filiform prolongation 
with which it becomes incorporated. Its outer 
border exhibits a series of tooth-like trian- 
gular processes which are inserted by their 
apices into the dura mater. The first pointed 
process, which is longer than the rest and less 
triangular in shape, is inserted into the dura 
mater on the margin of the occipital bone, 
where it stands in relation with some parts of 
interest. The posterior root of the sub-occi- 
pital nerve, and the filaments of origin and the 
resultant trunk of the spinal accessory, are on a 
plane posterior to it. The vertebral artery and 
the ninth pair of nerves are anterior to it. The 
number of teeth varies from eighteen to twenty- 
two. The last is attached to the dura mater 
about the level of the first or second lumbar 
vertebra. The points of attachment are be- 
tween the points of exit of the spinal nerves, 
being almost always nearer the lower than the 
upper nerve. The intervals between each pair 
of dentated processes vary in different regions of 
the spine as the distances between. the roots 
of the nerves vary. At its insertion into the 
dura mater each process pins down the visceral 
and parietal layers of the arachnoid membrane, 
probably piercing them to reach the fibrous 
membrane. At its lowest part, a little above 
the extremity of the cord, tie denticulated 
margin ceases, and the longitudinal portion 
may be traced downwards, gradually dimi- 
nishing in size, along each side of the filiform 
prolongation of the pia mater. 
The dentated ligament has to the naked eye 
