. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. NERVOUS SYSTEM. (NERVE.) 591 no means free from them, and they will be employed in the course of this article. Such are the only subdivisions of the nervous system which anatomy appears to warrant. Others have been proposed; but as they are founded upon physiological opinions which are as yet hypothetical, it is unnecessary to discuss them at present. Having thus given a brief and general account of the nervous system and of nervous matter, we proceed to consider the anatomy and phy- siology of this system under the foll
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. NERVOUS SYSTEM. (NERVE.) 591 no means free from them, and they will be employed in the course of this article. Such are the only subdivisions of the nervous system which anatomy appears to warrant. Others have been proposed; but as they are founded upon physiological opinions which are as yet hypothetical, it is unnecessary to discuss them at present. Having thus given a brief and general account of the nervous system and of nervous matter, we proceed to consider the anatomy and phy- siology of this system under the following divisions:—I. THE GENERAL ANATOMY OF NERVES. II. THE COMPARATIVE ANATOMY OF THE NERVOUS SYSTEM OR ITS DISPOSI- TION THROUGHOUT THE ANIMAL KINGDOM. III. THE ANATOMY OF THE NERVOUS CEN- TRES, THE GANGLIA, BRAIN, AND SPINAL CORD. IV. AND LASTLY, THE OFFICE OF THE NERVOUS SYSTEM AND THE FUNCTIONS OF ITS VARIOUS PARTS. NERVE.—(vsvgov, nervus; Germ, nerve; Fr. nerf.) The nerves perform the inttrnuncial office in the nervous system by maintaining communications between the various organs and tissues and the nervous centres. They are bundles of threads of various size, surrounded by sheaths of membrane, with more or less of areolar tissue interposed. The nerves of the cerebro-spinal system and of the great sympathetic exhibit such different characters as regards their anatomy, that they may be examined separately. Cerebro-spinal nerves.—In examining a cere- bro-spinal nerve, we find it invested by a sheath of membrane, which has adherent to its inner surface thin layers of areolar tissue which pass, like so many partitions, between the threads or fibres of which the nerve is composed. This sheath is commonly called the neurilemma; it is analogous to the sheath which surrounds mus- cles. Its office is chiefly mechanical, namely, that of binding the constituent fibrillae and fas- cicles of the nerve together, so as to protect them and to support the delicate plexus of capill
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