The following are the cerebral membranes that are found at the origin of the nerves; 1st. the dura mater forms for them a kind of canal in the fissure through which they go out, then it quits them entirely, and is partly lost in the cellular texture, and the remainder is reflected upon the edges of the opening and continued with the periosteum. The optic nerve is the only exception to this; it is accompanied in its whole course by a fibrous canal, which goes even to the sclerotic coat, which in this way, communicates with the dura mater. 2d. The tunica arachnoides surrounds every nerve at its origin with a fold formed oftentimes in the shape of a tunnel, the broadest part of which is at the origin. By carefully raising the brain, or by opening the dura mater of the spinal canal, we very easily discover this fold, which is continued to the osseous opening, through which the dura mater enters, it is then reflected upon the surface of this membrane corresponding with the brain, forming a sac between it and the nerve. Sometimes, as in the optic nerve and the motor externus, it penetrates the fibrous canal of the dura mater, and accompanies the nerve to the middle of the canal, which, consequently, is lined in part by the tunica arachnoides, and partly by the cellular texture. 3d. The pia mater is used in a manner that is difficult to understand, and which has not as yet been well explained. I shall speak of its continuity upon the nerves, in treating of their peculiar membrane. The nerves go over a more or less considerable extent before going out of the cranium or the spinal canal. 1st. The two that arise from the cerebrum are much longer within than without. 2d. Among those of the tuber annulare and its dependancies, the pathetic nerves are the only ones that remain any length of time in the cranium before they go out of it, and that have a greater extent there than externally; all the others go out almost immediately. 3d. The nerves of the spine have a much greater extent when examined lower down. Above, they become directly external; below, they are six inches long in the canal, and consequently pass many foramina before they arrive at their own; hence it happens, as has been observed by Jadelot, that if we avail ourselves of the spinous processes, on account of their prominence, to judge of the origin of the nerves in the application of the moxa, it is necessary, in the neck, in order to act upon a point corresponding with the origin of any nerve in particular, to take nearly the spinous process of the vertebra that corresponds numerically with the pair that we have in view, whilst in the loins it is much above this vertebra that the application should be made.