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as the corpora quadrigemina, the hemispheres, etc., and from one half of the cerebellum to the other. The fibres spreading out, as already mentioned, in the hemispheres toward the convoluted grey surface, will have had very various origins. Some may perhaps have come all the way from the extremities of the body, passing by the spinal cord, medulla oblongata, cerebellum, pons Varolii, thalami optici, etc.; others have originated in the grey matter of the cord, passing without a break through all the intervening centres; a third class may have had their rise in the grey matter of the pons, a fifth in the cerebellum, a sixth in the corpora quadrigemina; others in the thalami optici, or corpora striata; besides other more minute sources.

The arrangement may thus be seen to resemble the course of a railway train. The various central masses are like so many stations, where the train drops a certain number of passengers and takes up others in their stead, whilst some are carried through to the final terminus. A system of telegraph wires might be formed to represent exactly what takes place in the brain. If from a general terminus in London, a mass of wires were carried out to proceed towards Liverpool, and if one wire of the mass were to end at each station, while from the same station new wires arose, one for every station, farther on, a complete and perfectly independent connexion could be kept up between any two stations along the line."*

The nerves are divided into two classes, the spinal and the cerebral; the one passing into the body along the spinal cord, the other directly from the brain. The nerves go forth in pairs from the spinal cord, passing out on either side between the vertebrae. Of this class, there are thirty one couples. Each of these nerves is divided at its root, into two portions termed the anterior root and posterior

* Quain's Anatomy.