These classes nearly correspond with the simple and compound ganglions of Scarpa* and Meckel.f There are occasionally found ganglia on other nerves; thus, Mr. Swan r has noticed one on the posterior spinal nerve, where it is placed under the extensor tendons of the wrist. My friend Mr. Pilcher has also found in two subjects a gangliform enlargement on the internal nasal nerve, where it is lodged on the athmoidal bone.
It is necessary to remark that although the ganglia of the first class are placed on certain of those nerves which are commonly regarded as being subordinate simply to sensation, yet the highly important observations of Dr. AI. Ilall,§ which have, I conceive, opened an en tirely new field in physiology, render it doubt ful that those bodies are essential to the exer cise of sensation.
Organization.—Although the eerebro-spinal and sympathetic ganglia present some impor tant peculiarities when contrasted with each other, particularly as regards the proportions of the grey and fibrous substances, still as both classes possess essentially the same struc ture, they may with propriety be considered in a collective manner.
Every ganglion contains two totally distinct substances which have a close relation to, and are, I believe, identical with the grey and fibrous matters, constituting the encephalon and other parts of the nervous system. It is true that the appearance of these bodies is in many respects dissimilar to that of the brain ; but at length it is universally admitted that differences in mere physical properties are unimportant, and do not constitute any test as to the essential structure of an organ. In the present instance the diversity may very readily be understood when the difference of situation is considered. The cerebral organ is enclosed in a cavity, the cranium, formed of some of the strongest boues of the skeleton, and hence, being effectually defended from the effects of motion and external pressure, all its parts are soft and delicate; whilst the ganglia, placed ou bones which move on each other, slightly it is true, are exposed to external compression, and consequently a much firmer texture is required. It is for this reason that these bodies are invested in a dense fibrous capsule, which is to them what the cranium is to the encephalon, and which furnishes in addition a number of internal processes surrounding each fibril, and sustaining the spherical masses of grey matter. The difficulty of detecting
the intimate texture is by these means greatly increased ; but as it is so similar to that of the cerebrum, it is desirable to examine the con stituent parts according to the order observed in investigating that organ.
I. Reddish grey matter.—The quantity of this substance, often called the peculiar matter of the ganglions, but which, as I have stated, is possessed by those bodies in common with the brain and spinal chord, is very considerable, constituting apparently the largest, and cer tainly the most essential part of the ganglion. It is so intimately connected with the fibres that these latter appear as if they were incrusted, being surrounded in every direction by this Freyish matter; but although this intimate intermixture is very evident, no fibrils can be perceived actually terminating in or arising from the grey matter. A section of one of the sympathetic ganglia, the first cervical for ex ample, displays this incrustation of the fibres and the interposition between them of rounded masses of the grey matter ; but the Gasserian is in many respects the most favourable for ex amination.
Much difference of opinion exists concerning the true nature of this substance. Scarpa con tends that it is not analogous with the grey matter of the brain, but that it consists of a flocculent tissue loaded with a mucilaginous fluid, vrhich becomes oily in obesity, and watery and abun dant in anasarca. The accumulation of fat in the true ganglionic tissue has, however, been denied by Bedard, Wutzer, and others. Ac cording to I%ichat, whose opinions must always command our respect, "the ganglions have a colour very different from that of the nerves. They present a soft spongy tissue, somewhat similar to the lymphatic glands, but which has nothing in common either with the cerebral substance or with that of the nerves." It is stated by Lobstein, who has published one of the latest and most minute accounts of the structure and diseases of the sympathetic nerve,* that he has observed lying contiguous to the white and filamentous tissue another substance presenting a flocculent appearance, with globules interspersed (matcries ref sub stantia orbicularis twnentosa), and which he regards as the second material of the ganglia.