NERVOUS SYSTEM. (Nerve.) 
characters, with the peculiar construction of 
the peripheral expansion, would induce me to 
regard what is generally described as the optic 
nerve as a process of the brain itself, around 
the peripheral portion of which a dioptric appa- 
ratus has been disposed in order to produce 
those refractions in the rays of light which are 
necessary to the formation of an image upon the 
retina. And my friend, Mr. Bowman, has been 
led to adopt a similar conclusion from examin- 
ing the structure of the retina and optic nerve. 
Olfactory nerves.—The true olfactory nerves 
are very numerous and pass from the bulb of the 
olfactory process or olfactory nerve of descrip- 
tive anatomists. The peculiar characters of this 
process, as distinguishing it from a nerve properly 
so called, have long attracted attention. In truth, 
this process has the characters of a portion of 
the brain in a much more obvious way than the 
optic nerve, for it contains a larger portion of 
grey matter which adheres as a distinct layer to 
e white matter, as in the formation of the 
convolutions; and, moreover, its anterior ex- 
tremity or bulb contains a ventricle which may 
easily be demonstrated in a recent brain. It is 
from this bulb that the minute threads, which 
_ may be properly called olfactory nerves, take 
their rise and pass down through the foramina 
of the cribriform plate. Nothing satisfactory 
is known as to the disposition of the ultimate 
‘ramification of these nerves upon the Schnei- 
_ derian mucous membrane. 
The statement of 
_ Valentin that they form loops similar to those 
of cutaneous nerves is probably correct. It is 
not improbable that the papilla described by 
reviranus were particles of columnar epithe- 
ium to which cilia are attached. 
_ Auditory nerve.—The auditory nerve exhibits 
characters sufficiently distinct from the portio 
dura of the seventh, beside which it lies, to have 
Ted the anatomists of former days to separate it 
under the name of portio mollis. In fact, it pos- 
Sesses all the appearance of cerebral substance, 
and it wants the fasciculated disposition which 
Mere nerves exhibit. Its fibres are delicate 
and very prone to become varicose, and, as in 
the case of the olfactory process, it passes out 
of the cranium, not as a trunk, but by means 
of several minute filaments of various size 
which pee the foramina of the cribriform 
floor of the internal auditory foramen. Most 
observers express themselves in favour of the 
Opinion that the terminal filaments are disposed 
in a looped form upon the membranous laby- 
rinth and the cochlea. Valentin describes and 
delineates a plexiform arrangement, with loop- 
ings ofsome of the primitive fibres ; others ofthem, 
however, he says, do not affect this disposition, 
but appear to have free extremities. And this de- 
Scription corresponds with that which Henle has 
given. This author states that from researches 
which he has made upon the lamina spiralis of 
mammifera and the ampulle of the frog, he has 
no doubt of the existence of fibres which pass 
from one fascicle to another in a looped form ; 
but he finds it difficult to determine whether all 
the tubes contained in each fascicle form 
similar loops. Wagner delineates the looped 
arrangement, and Pappenheim adopts the 
same view. Mr. Wharton Jones states that 
597 
the tubular structure of the ner{us fila- 
ments ceases among grains of nervous matter, 
arranged into a sort of expansion, (see OrGan 
or Hearne), and he denies the existence of 
an arrangement in loops. My own observation 
leads me to concur in this description; and I 
would add that there seem to be here, as in the 
retina, some elements of the grey nervous 
matter scattered among the primitive filaments. 
This fact did not escape Valentin, for he 
remarks the existence of ‘“ very large globules” 
among the primitive fibres, similar to what he 
and Purkinje had noticed in the grey matter of 
the olfactory bulbs.* If this view of the peri- 
pheral expansion of the auditory nerve be cor- 
rect, its analogy with the optic is very obvious; 
and it may be conjectured of the ear, as in 
reference to the eye, that around a process from 
the brain an apparatus has been organized fitted 
to transmit and modify sonorous undulations, 
In the present state of observation we should 
not be justified in making any positive state- 
ment with reference to either the central or 
peripheral connexions of the nerves, beyond the 
following: that at the centres the grey and white 
elements are always associated, and that nerves 
may be truly said to arise out of grey matter; and 
that at the periphery, the nervous fibres, which 
in their progress from centre to circumference 
were bound together, become separated, and 
connect themselves, probably by intimate ad- 
hesion, with the elementary parts of the tissues 
and organs to which they are distributed. 
Of the ganglionic nerves.—Without more 
exact information respecting the minute ana- 
tomy of these nerves, our knowledge of the 
peculiar function of the ganglionic system must 
be very incomplete. The following questions 
suggest themselves in reference to this system. 
1. Are its anatomical characters sufficiently 
distinct from those of the cerebro-spinal system 
to warrant us in separating it from that system, 
if only for purposes of description? 2, Is it 
an independent system, as some have conjec- 
tured, giving fibres to the cerebro-spinal nerves 
as well as receiving some from them. 3. If it 
be an independent system, wherein consist the 
peculiar features by which its fibres are to be dis- 
tinguished from those of cerebro-spinal nerves ? 
There are many features belonging to this 
system which justify its separation from that of 
the brain and spinal cord. The great number 
of ganglions connected with it, suggests the 
propriety of designating it ganglionic system, 
nor does the existence of ganglions on the pos- 
terior roots of spinal nerves render this appella- 
tion less proper; for in this system every nerve, 
nay every fibre, is connected with or passes 
through one or more ganglions. The external 
aspect of these nerves is very characteristic. 
Their neurilemma is very dense, and has more 
of the silvery appearance of white fibrous tissue 
than the sheaths of cerebro-spinal nerves; they 
want the fasciculated character of the latter 
nerves, and their colour has a diffused greyish 
or greyish red hue. The smaller ramifications 
are exceedingly delicate and appear to be soft, 
* Valentin, tiber den Verlauf und die letzen 
Enden der Nerven, p. 
