ABNORMAL ANATOMY OF NERVES.—CeIthill nerves are sometimes absent, from a defect in the developement of the org-an to which they are devoted ; as the optic nerve, or the olfac tory, when their respective organs are wanting. The uon-developement of the eye will also cause a non-developement of the fourth pair and the other orbital nerves which influence the II movements of the eyeball.
The morbid states of nerves are few and rare. Inflammation of a nerve rarely occurs idiopa thically or primarily. Occurring from what ever cause, it would be distinguished by hyper mnia, enlargement, and by deposit of more or less of lymph or pus. In the acute inflam mation the nerve would be softened; but in the chronic it would become indurated. Abscess of a nerve is of very rare occurrence.
Inflammatory affections of nerves occur chiefly in connexion with rheumatic or gouty states of the system. Sciatica is, no doubt, an in flammatory affection of the sciatic nerve of the gouty kind. In lumbago probably the mus cular nerves of the lumbar muscles are similarly affected.
Atrophy is a condition into which nerves may fall from disuse or from pressure. In it the nerve-fibres shrink, their central axis wastes, and in extreme cases disappears entirely, the tubular membrane becoming plicated and as suming the characters of fibrous tissue. The nerve experiences a great diminution in size, and the wasting is obvious to the naked eye.
Hypertrophy. —Whether a nerve becomes enlarged when more work is thrown upon it, as a muscle does, is as yet quite uncertain. I
am disposed to think that the nerve-fibres may acquire some increase of size; but it seems to me impossible that they should become more numerous. The number of nerve-fibres in in dividual nerves, as that of muscular fibres in almscles, is probably determined at their pri story developement,* and they undergo no ahange but that of length and thickness subse 9uently. It would not be difficult, by destroy g the office of the vagus nerve on one side, ascertain whether, after the lapse of some time, the other, upon which its function would devolve, acquired any increase in the size of its nerve-fibres.
Certain gangliform tumours are formed upon nerves, to which the term neuroma has been applied. They consist of areolar tissue and of nerve-fibres, and seena to be formed by an increased developement of the areolar tissue between the nerve-fibres. These tumours vary considerably in size and number ; sometimes they are not larger than a filbert or a gooseberry sometimes as large as a walnut. In genera they are few and limited to one nerve, and their size is proportionate to that of the nerve with which they are connected. In a few rare cases tumours of this kind have been found in im mense numbers scattered over the vvhole cere bro-spinal system.
(R. B. Todd.)