This paper is the first of three communications, in which is shewn the distinctions in the regular series of nerves arising from the spinal marrow, and the ten nerves which arise directly from the brain.

The author remarks, that unless we comprehend the reason of the perfect symmetry of the spinal nerves, as contrasted with the irregularity of the encephalic nerves, we must confess ignorance of much of the structure of the animal frame.

After a general view of the nerves arising from the base of the brain, and assigning the reason of their apparent irregularity, he enters on the investigation of the third nerve. He shews that it arises from the distinct columns of which the crus cerebri is composed, by courses of parallel filaments; and that these afterwards compose a dense structure resembling ganglion.