PHYSIOLOGY OF THE NERVOUS SYSTEM. 
the generative instinct and the cerebellum, from 
the occasional existence of an abnormal erection 
of the penis, is not justified by the facts. This 
symptom is far from being constant in cerebellar 
disease—indeed it occurs in but a very small 
number of cases—and, as a symptom pomting 
to lesion of a particular portion of the cerebro- 
spinal axis, it is much more indicative of 
disease of the medulla oblongata or of the 
cervical portion of the spinal cord. 
Office of the cerebral convolutions—The 
great sheet of vesicular matter which forms the 
cortex of the human brain, is of such vast 
extent that it is forced to assume the convo- 
luted form in order to its being packed within 
the ordinary compass of the cranium. A little 
consideration will shew that the convoluted 
Jorm can be regarded no otherwise than as a 
convenient mode of packing, and that the 
number and depth of the convolutions are the 
best indications of the superficial extent of this 
expanse of vesicular matter. In certain cases 
a slow and gradual accumulation. of water 
within the ventricles of the brain, causing a 
corresponding enlargement ‘of the cranium, 
expands the matter of the cerebral hemispheres, 
by which the ventricles are enclosed, and the 
convolutions become unfolded. We thus ob- 
tain a distinct demonstration of the true arrange- 
ment of this part of the hemisphere, which 
must be regarded as a nervous centre, con 
sisting of a vast mass of the potential vesi- 
cular matter freely supplied with bloodvessels 
from a vascular surface on its exterior (the pia 
mater), and giving rise to an infinite multitude 
of nerve-fibres, which pass from its internal 
Surface to the corpora striata and optic thalami, 
the centres of volition and sensation. The 
name which Mr. Solly has given to this ex- 
panse of nervous matter, hemispherical gan- 
glion, is very expressive, not only of its true 
cter as a centre of nervous power, but 
likewise of the wnity of the organ on each side, 
‘consisting as it does of an uninterrupted layer 
of vesicular matter with its emerging or im- 
merging fibres, and not of a great number of 
a" organs, as the term convolutions would 
imply. 
This vesicular surface with the fibrous matter 
which connects it with the optic thalami and 
corpora striata forms by far the largest portion 
of the encephalon in the higher classes of 
animals. This fact alone ought to stamp it 
with great physiological importance. Bot, 
further, it is a well-proved fact, that the com- 
plexity of the convolutions in the animal scale 
% in the direct ratio with the advance of in- 
telligence. At the same time it must be re- 
membered that the complexity of the convo- 
lutions is in part determined by the size of the 
head and the capacity of the cranium. If, for 
example, the habits and mode of life of the 
animal require a small head and at the same 
time a certain degree of intelligence, the brain 
would exhibit a greater number and complica- 
tion of convolutions than would be found in 
an animal of corresponding intelligence, but 
which required and possessed a larger head. 
Hence neither the size nor the weight of the 
722x 
brain, whether absolute or in relation to the 
body, affords any certain criterion of the extent 
of the convoluted surface. Highly complicated 
convolutions may exist along with a brain 
both absolutely and relatively small. Thus, the 
ferret, as shown by Leuret, whose habits require 
a small head, has several well-marked convo- 
lutions on each hemisphere, and a brain no 
larger than that of the squirrel, which has no 
convolutions at all, and which wants even the 
few fissures which mark their first develope- 
ment in the rabbit, the beaver, the agouti, &c. 
And the last-named animals have the brain 
both absolutely and relatively larger than that 
of the cat, the pole-cat, the roussette, the 
unau, the sloth, and the pangolin, all of which 
possess convolutions. 
At the early periods of human life, in in- 
fancy and childhood, the convyolutions of the 
brain are very imperfectly developed, but their 
increase of size goes on simultaneously with 
the advance of mental power. If the former 
be arrested, or if some congenital fault pre- 
vent the further growth of the convolutions, 
the mental powers are of the lowest and fee- 
blest kind, but little or not at all above those 
of the brute with imperfect convolutions. In 
all idiots the brain is not only small, but its 
convoluted surface is extremely limited. 
Anatomy points to the conclusion that the 
office of the convolutions is connected with the 
functions of the mind. Perception, memory, 
the power of abstraction, judgment, imagina- 
tion, all possess, as instruments of corporeal 
action, these folds of vesicular matter. And 
it seems not improbable that the phrenological 
view which assigns to certain convolutions a 
special office connected with some particular 
faculty or faculties is true. This is strongly 
supported by the fact of a regular disposition 
of certain primary convolutions im the various 
classes of animals, so that each form of brain 
has its proper convolutions, and that in tracing 
the convolutions from the most simple to the 
most complex, indications are found of the 
persistence of the primary and fundamental 
convolutions in the midst of many secondary 
and superadded ones. 
It may be here mentioned that Gall was by 
no means the first to assign this function to the 
convolutions. Our countryman, Willis, in the 
seventeenth century, distinctly advanced this 
opinion, and conjectured that the various gy- 
rations were intended for retaining the animal 
spirits “for the various acts of imagination 
and memory” within certain limits. 
It is important to ascertain the endowments 
of the fibres which connect the vesicular sur- 
face of the convolutions to the corpora striata 
and optic thalami. They might be supposed to 
possess similar endowments to those of sensi- 
tive and motor nerves, if we adopted the views 
of those who hold that all the nerves are con- 
tinued up into the brain. This point, however, 
has been settled in the most decisive manner by 
experiments, dating as far back as the time of 
Lorry.* Mechanical injury to them excites 
* Mém. de l’Acad. des Sciences, 1760, 
