PHYSIOLOGY OF THE NERVOUS SYSTEM. 
interference is removed, or kept under con- 
trol, physical actions develope themselves ; 
being effected through the same nerves as those 
which volition influences or which sensitive 
impressions affect. The latter are, in such 
instances, the excitors of the former, no doubt 
through the vesicular matter in which they are 
implanted. These actions become most mani- 
fest when the connection of the brain with the 
spinal cord has been severed; and they occur 
in the most marked way in those situations 
where the cutaneous nerves are so organized 
as readily to respond to the application of a 
stimulus applied to the surface, or they be- 
come universal when the cord is in a state of 
general excitement. 
The movements in locomotion and the main- 
tenance of the various attitudes are effected 
through the ordinary channels of the physical 
and volitional actions; and the posterior co- 
lumns of the cord, by their influence on the 
vesicular matter of the segments in which the 
nerves are implanted, co-ordinate and _har- 
monize the complicated muscular actions of 
the limbs and the trunk under the controul of 
that portion of the encephalon which probably 
is devoted to that purpose. This power of co- 
ordination is probably mental, and - intimately 
connected with the muscular sense. 
Functions or THE ENncEPpHaton. — It 
will be convenient first to examine the func- 
tions of those parts of the encephalon which in 
structure most nearly resemble the spinal cord. 
Functions of the medulla oblongata, mesoce- 
phale, corpora striata, and optic thalumi.— 
The medulla oblongata most nearly resembles 
the cord in form and structure, at the same 
time that it exhibits most marked and impor- 
tant differences from it. Its subdivisions form 
connections superiorly with other parts of the 
brain, namely, the mesocephale, corpora striata, 
and optic thalami. These connections are so 
intimate, that, however convenient it may be to 
the descriptive anatomist to describe these 
parts each by itself, it is impossible, in exa- 
mining into their functions, to separate them 
completely. The functions of one part are so 
readily affected by a change in any or all of 
the others, that the effects of experiments are 
not limited only to the part operated upon, but 
affect or are affected by the rest. Thus, the 
olivary columns, which form the central and 
most essential part of the medulla oblongata, 
extend upwards through the mesocephale to 
the optic thalami; and the anterior pyramids 
form an intimate connection not only with the 
vesicular matter of the mesocephale, but, to a 
great extent, with that of the corpora striata. 
All these parts taken together, with the quadri- 
geminal tubercles, will be found to be the 
centre of the principal mental nervous actions, 
and of certain physical actions. which are very 
essential to the integrity of the economy. 
The office of the nerves which arise from this 
segment of the encephalon throws light upon 
its function. These nerves are partly destined 
for respiration, partly for deglutition, and partly 
also for acts of-volition and sensation. 
722t 
Destruction of the medulla oblongata is fol- 
lowed by the immediate cessation of the pheno- 
mena of respiration ; and this takes place whe- 
ther it be simply divided, or completely re- 
moved. When an animal is pithed, he falls 
down apparently senseless, and exhibiting only 
such convulsive movements as may be due to 
the irritation of the medulla by the section, or 
such reflex actions as may be excited by the ap- 
plication of a stimulus to some part of the trunk. 
If, in an animal which breathes without a 
diaphragm, as in a bird or reptile, the spinal 
cord be gradually removed in successive por- 
tions, proceeding from below, up to within a 
short distance of the medulla oblongata, loss of 
motor and sensitive power takes place succes- 
sively in the segments of the body with which 
the removed portions of the cord were connected. 
But the animal still retains its power of per- 
ceiving impressions made on those parts of the 
body which preserve their nervous connection 
with the medulla oblongata, and continues to 
exercise voluntary control over the movements 
of those parts. The movements of respiration 
go on, and deglutition is performed. The 
higher senses are unimpaired.* 
These phenomena are sometimes observed in 
man—in such cases as that alluded to in a 
former page; where, from injury to the spinal 
cord in the neck, below the origin of the phrenic 
nerve, the patient appears as a living head with 
a dead trunk. The sensibility and motor 
power of the head are perfect; respiration goes 
on partially, and deglutition can be readily 
performed. The senses and the intellectual 
faculties remain for a time unimpaired. 
Irritation of any part of the medulla oblon- 
gata excites convulsive movements in muscular 
parts which receive nerves from it, and, through 
the spinal cord, in the muscles of the trunk. 
Spasm of the glottis, difficulty of deglutition, 
irregular acts of breathing, result from irritation 
of the medulla oblongata; and, if the excite- 
ment be propagated to the cord, convulsions 
will become more or less general. 
If a lesion affect one half of the medulla ob- 
longata, does it produce convulsions or paralysis 
on the opposite side of the body? This ques- 
tion may be certainly answered in the affirma- 
tive, when the seat of the lesion is in the conti- 
nuations of the columns of the medulla oblon- 
gata above the posterior margin of the pons. 
It is not so easily solved, however, when the 
disease is situate below the pons. The results 
of experiment on this subject are contradictory, 
owing probably to the extreme difficulty of 
limiting the injury inflicted to a portion of the 
medulla on one side; and those of Flourens 
are of no value for the decision of this question, 
as it appears that he injured chiefly the resti- 
form bodies. Anatomy suggests that a lesion 
limited to either anterior pyramid would affect 
the opposite side of the trunk, for it is known 
that such an effect follows disease of the conti- 
_ nuation of it in the mesocephale or crus cerebri ; 
and that lesion limited to the posterior half of 
* Flourens, p. 179. 
