haryngeal, which are freely distributed 
pon the mucous surface of the pharynx. This 
stimulus causes a change in the medulla ob- 
longata, in which those nerves are implanted, 
and that change is propagated thence by the 
pharyngeal branches of the vagus to the mus- 
cles which contract the pharynx in the act of 
deglutition. 
n such an action the change in the nerves 
by which the muscular contraction is excited 
must take place in a two-fold direction,—first, 
from the circumference to the centre, from the 
point of application of the stimulus to that at 
which the nerves become implanted in the 
centre; and, secondly, from centre to circum- 
ference, from the point at which the stimulus 
falls upon the centre to that where the nervous 
fibres mingle themselves with the muscles of 
the part to be moved. The stimulus, which is 
incident upon the nervous centre, is said to be 
reflected 3 it to the muscular textures, the 
immediate agents of the required movement. 
Hence Dr. Marshall Hall has proposed to dis- 
tinguish a special system of incident and reflex 
nerves, or of excito-motory nerves, the former 
being exrcitor, the latter motor. ‘This distine- 
tion, considered anatomically, is as yet quite 
hypothetical, for we have no unequivocal proof 
that the nerves of sensation and volition, which 
in their ordinary mode of action are ufferent 
and efferent as regards the brain, may not be 
competent by the relation which they must 
necessarily bear to the spinal cord, to perform 
the actions which are thus assigned to a dis- 
tinct system. The determination of this point 
depends more upon the solution of certain pro- 
blems respecting the anatomical constitution 
of the nervous centres, than upon any purely 
physiological experiments. It will be made 
the subject of careful examination at a subse- 
quent part of this article. 
The great peculiarity of this class of nervous 
actions is their independence of the mind. An 
act of the mind forms no necessary part of their 
mechanism. At the same time there are certain 
of them which do not take place without the 
mind being conscious of the change. The act 
of deglutition above referred to, although quite 
independent of the mind, does not generally 
take place without being felt. But the change 
in the pupil, consequent upon the stimulus of 
light acting through reflex nerves upon the iris, 
is not at all perceived by the individual, and is 
therefore in every respect independent of mental 
change. Let it be remembered, then, that 
there are some physical nervous actions which 
the mind is not conscious of, and others of 
which the mind will always, or at least generally, 
take eognizance. 
We may conclude this brief reference to 
nervous actions by the following classification 
of them :— 
Psychical or mental nervous actions :— 
Actions of perception. 
Actions of emotion. 
Actions of volition. 
Physical nervous actions :— 
Actions from a physical change originating in 
the nervous centre; as in disease. 
590 
& 
u 
NERVOUS SYSTEM. (Nervous Actions.) 
Reflex actions— 
a, with consciousness. 
b, without consciousness. 
Anatomical subdivision of the nervous sys- 
tem.—The nervous centres, as they are four 1 
in the Vertebrate series, are distinguished as t 
brain, or encephalon, the spinal cord (medulla 
spinalis ), the ganglions. In the Invertebrata, 
the centres all bear the anatomical characters of 
ganglions, although, doubtless, they present 
some analogy in office to those specially distin- 
guished among Vertebrata. Their arrangemen 
varies considerably according to the differe 
of form of the various invertebrate classes. 
The brain and spinal cord, and the s 
of nerves connected with them, constitute the 
cerebro-spinal portion of the nervous system 
which Bichat distinguished as the nervous 
tem of animal life, a distinction which, as i 
was dependent on his untenable hypothesis of 
the two lives, ought now to be discarded. The 
only subdivision of the nervous system c 
can be conveniently adopted must rest upoi 
the basis of anatomy. There is not a sufficient 
distinctness of function in different portions 
the nervous system to justify the separation 0 
them on physiological grounds. Di 
There are very numerous ganglions connecte 
with the cerebro-spinal system. These are tl 
ganglions on the posterior roots of spinal n 
the ganglion of the fifth pair, 
glosso-pharyngeal, and of the vagus. They 
conveniently distinguished as cerebro 
ganglions. 
A large portion of the nervous system 
made up entirely of ganglions, with their e 
necting cords and nerves, which ramify in 
plexiform manner among various internal vis 
and upon the coats of bloodvessels. In 1 
vertebrated animals, where it is highlyd yp 
it is disposed as a chain of ganglia on each | 
of the spine, and at the base of the skull, r 
the foramina, through which the spinal 
encephalic nerves pass out; and at all 
situations it forms a very intimate conn 
with the nerves of the brain and spinal coi 
This portion of the nervous system exh 
many peculiarities referable to its compe 
its mode of arrangement, and its conneé 
with the organs among which its nerves ran 
which, at least, entitle it to be considered ¢ 
from the cerebro-spinal system; and 
so far as to affirm its entire independen 
that system, and to assign to it a peculiar a 
different from that of the nerves connectec 
the brain and spinal cord. Bichat calls 
nervous system of organic life. Previ 
time it was known as the great 
(nervus intercostalis), the great sympe 
nerve (nervus sympathicus magnus ), and 
it is very commonly described under the 
name. The term visceral nerve has also 
proposed for it. It has also been distingui 
as the ganglionic system. It is diffieult to fit 
an unexceptionable name for it which does 
involve the adoption of some theory resf 
its function. On the whole, the terms sympat! 
nerve and ganglionic system are those ¥ 
appear liable to fewest objections, although 
oc 
