Obrázky na stránke

These broad fascicies or pyramids are, as diverging nerves, subject to the necessity of passing through ganglia ; and they in fact pass through two of thein.

The first of these is the pons Varolii seu protuberantia annularis Willissii. This is, in part, a commissure of the diverging nerves of the cerebellum (which may be here anticipated) and in part a ganglion of the fascicles forming the hemispheres.

Even on the outside of the pons Varolii, but still better if (the brain being reversed)a slight superficial incision be made in it in the direction of the pyramids towards the crura cerebri, and the edges of this incision be carefully drawn from each other; the diverging nerves of both hemispheres of the cerebellum

may be seen running across and meeting in the pons (or bridge) as their com

If these transverse striz be pursued with the handle of a scalpel, or with a concave scalpel, somewhat deeper in the substance of the bridge, there will be met about one or two lines below the surface a layer of neryous fibres, running in a line from the pyramids to the crura cerebri. Betwixt these nervous fibres running along through the bridge and those transverse striæ, is to be seen the cortical or cineritious sub. stance which covers the extreme surface of the nervous membrane, and forms, as it were, its last ganglion, as the organ of nourishment to the oblong fibres, which issue out of the bridge in a strikingly greater mass than they enter into it from the pyramids. If this layer of nervous fibres which runs from the pyramids along the pons Varolii be removed, a layer of transverse striæ is met with, which .striæ returning from the two halves of the cerebellum, meet together in the bridge as their commissure. This layer of transverse striæ is succeeded again by an oblong layer of nervous fibres issuing from the pyramids.



Gall has at present discovered eleven layers of these nervous fibres, proceeding from the pyramids through the pons Varolii.

After the nervous fibres of the pyramids have in this way passed through the pons Varolii, as their first ganglion, and issued out of it much encreased, they form the crura cerebri, which, as observation teaches, are nothing but a continuation of the pyramids, or that pair of nervous fascicles which forms the hemispheres of the cerebrum.

The nervous fibres which form the crura cerebri, before they pass into the membrane, the folds of which constitute the hemispheres, pass through a second ganglion, that is, the


[ocr errors]

cut away.

ganglion of the cerebrum, a part of the brain, the real form of which has been hitherto unknown, and still "less its internal quality, but which is discovered at once when the middle lobe of the brain by the Fossa Sylvii is

The whole congeries of the brain, and also the optic nerve around this, may be taken away. This optic nerve winds on each side of the front pair of the four eminences which are its first ganglion from behind, round that grey mass which forms the ganglion of the cerebrum, towards the front, in order to form the decussatio nervorum opticorum. Seen from above, or from the great ventricles or cavities of the brain, it is the thalami nervorum opticorum (which are nothing but a web of all the nervous fibres in the ganglion of the cerebrum, or are properly the ganglion itself). and the corpora striata, (which are properly the nervous fibres already diverging from this ganglion) which constitute the ganglion of the cerebrum.

That is, this ganglion consists of two pulpy inasses crossed in the middle by the nervous fibres which spring from the pyramids, and have been strengthened by passing through the pons

Varolii. If the brain be reversed, and the upper pulpy mass be carefully taken away, the nervous fibres can be traced from


the crura cerebri entirely through the ganglion of the cerebrum. Each of the nervous fibres which are then seen forins a particular involution of the brain, and is to be considered as the


of some intellectual function. After these nervous fibres have passed through the ganglion of the cerebrum enlarged, they diverge on all sides through the distinct involutions of the cerebrum, and forming a nervous membrane over the pulpy cortical substance which surrounds the whole brain on which they are spread, terminate in this pulpy matter, which constitutes, as it were, their last ganglion *.

In the same manner as the diverging nervous fibres of the cerebrum and cerebellum terminate, terminate also the diverging fibres of the other nerves which spring from the spinal marrow, in a pulpy substance, which is, as it were, their last ganglion, and in different places of different qualities. In the labyrinth, the pulpy mass, in which the progressive fibres of the auditory nerve terminate, appears like a transparent gelatinous body; in the nose, the pulpy mass in which

* Here the German writer has inserted marks of interrogation (??). An expeditious style of commenting, not unusual in German works, where the editor differs in opinion from the author. C3


the diverging fibres of the olfactory nerve terminate, appears like a serous skin, the pituital membrane, &c. In some places this substance is woven into a hardish web of nerve, as, for instance, in the ganglion of the cerebrum (the corpus ciliare) and in the ganglion of the nervi accessorii et oculo-motorii, (the corpus olivare). In other places it lies like a grey pulpy substance, as, for instance, in the ganglion of the cerebrum and on the surface of the cerebrum and cerebellum.

Out of this pulpy mass in which, as before stated, the diverging nerves of the cerebrum, cerebellum, &c. terminate, the other kind of nerves arise; whether it be that the diverging nerves turn back again and converge, or altogether independently of them ; that is, a second species of nerves is found, viz. 2. The converging nerves and congeries which


be thus characterized : a.) That they are softer than the diverging

of nerves,


b.) That they take their origin in that pulpy mass in which the diverging nerves terininate.

c.) That they unite and strengthen themselves in an inward direction, that is, from the surface of the brain, &c. to the spinal marrow; but they do not, like the diverging


« PredošláPokračovať »