Outlines of human physiology; designed for the use of the higher classes in common schools . re, a continuation of the brain, and resembles it veryclosely in its structure. It is covered by a firm mem-brane, and the canal which encloses the whole, is sostrong, and so well supported, that the injuries of thespinal cord are not very frequent. The nerves are white cords of medullaiy matter, thatare connected with the brain and spinal marrow. Thereare no less than twelve pairs from the brain, and thirtypairs from the spinal marrow. It has been usual, tillrecently, to say that there were but nine p
Outlines of human physiology; designed for the use of the higher classes in common schools . re, a continuation of the brain, and resembles it veryclosely in its structure. It is covered by a firm mem-brane, and the canal which encloses the whole, is sostrong, and so well supported, that the injuries of thespinal cord are not very frequent. The nerves are white cords of medullaiy matter, thatare connected with the brain and spinal marrow. Thereare no less than twelve pairs from the brain, and thirtypairs from the spinal marrow. It has been usual, tillrecently, to say that there were but nine pairs of cere-bral nerves, or nerves of the brain, but the subdivisionthat has been made of some of them, and which in-creases the number to twelve, is now generally the nerves are enclosed in a sheath. Their fibrous12* 138 NERVOUS SYSTEM. Structure is more evident than that of the spinal cord,or even than that of the brain itself. The nerves soon subdivide and communicate freelywith each other, forming a sort of net-work, known bythe name of plexus. New nerves go off from the. Base of the Brain. plexuses, which seem to be independent of the originalones which entered into their structure. The nervesof the brain are principally distributed to the organs ofsense, and those of the spine to the muscular parts. NERVOUS SYSTEM. 139 The ganglions are small bodies of a reddish color onthe exterior, but white within, that are found along thecourse of some of the nerves. They resemble some-what the brain in their structure, being composed of twoparts of different colors- It is generally admitted thatthe nerves that go from them are larger than those thatentered them; as if they imparted to the nerve someadditional power. This cursory view of the structure of the nervoussystem, may perhaps be sufficient to render more intel-ligible the account that w\\\ now be given of its functions. The brain is the material agent of the mind, and it isalso the organ which perceives the impre
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