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LEFT NERVE 414 NESS NEBVE, or NERVOUS SYSTEM. A nerve is one of the fibers which pro- ceed from the brain and spinal cord, or from the central ganglia of lower ani- mals, and ramify through all parts of the body, and whose function is to con- vey impulses resulting in sensation, mo- tion, secretion, etc. The aggregate of these nerves, and the centers from which they proceed, forms the nex'vous sys- tem, the medium through which every act or detail of animal life is inaugu- rated and directed. The essential idea of any nervous system involves the neces- sary presence, firstly, of a nerve center or centers, which generate the nervous force or impulse; secondly, of conduct- ing fibers or cords, the nerves; and thirdly, of an organ, part, or structure to which the impulse or impression may be conveyed. The nerve-centers of man and vertebrates generally are disposed so as to form two chief sets, which are to be regarded as essentially distinct. The brain and spinal marrow together (see Brain) constitute the first of these centers, and are collectively in- cluded under the name cerebro-spinal system or axis. The second system is the sympathetic or ganglionic. From each of these systems nerve-cords are given off — the cerebral and spinal nerves from the former; and the so- called sympathetic fibers from the latter. The brain and spinal cord are contained within the continuous bony case and canal formed by the skull and spinal column; while the chief masses of the sympathetic system form an irregu- larly disposed chain, lying in front of the spine, and contained within the cavi- ties of the thorax or chest and ab- domen. The general functions of the cerebro-spinal system are those con- cerned with volition and muscular move- ments, with the control of the senses, and in higher forms with the opera- tions of the mind. The nerves of the sympathetic system in chief are dis- tributed to the viscera, such as the heart, stomach, intestines, blood-vessels, etc.; and the operation of this system is in greater part of involuntary kind, and without the influence or command of the will. The cranial or cerebral nerves pass from the brain through dif- ferent openings in the skull, and are all in pairs, the first pair being the olfac- tory nerves or nerves of smell; the sec- ond, the optic nerves, or nerves of sight; while others have to do with hearing, taste, general sensibility, and muscular motion. The spinal nerves, after is- suing from their openings in the ver- tebral column, split into two divisions, one of which proceeds to supply parts behind the spine, while the other passes toward the front. The first eight spinal nerves on each side are called cervical, the next 12 are dorsal, the next five lumbar, then five sacral, and one coccygeal. The general functional relation of the nervous system may be summarized by stating that its functions comprehend the reception and distribution of im- pressions; that these impressions origi- nate either from influences acting on the periphery, or from the nerve-cen- ters, brain, or mind; these impressions respectively influence or stimulate the mind or nerve-centers, and the muscles or secreting structures; and lastly, that all nervous phenomena are exerted through or accompanied by nervous ac- tion, and that this latter is, so far as physiology has yet been able to de- termine, of a uniform and similar kind. See also Eye; Ear; Nose; etc. The Invertebrate possess no such specialization of the nervous centers as is seen in Vertebrates, in which the brain and spinal cord are inclosed with- in their bony case and canal, and thus shut off from the general cavity of the body. The great and distinctive fea- ture between the nervous system of Vertebrata and that of the lower forms consists in the absence of a defined or chief nervous center, through which con- sciousness may intervene to render the being intelligent, and aware of the na- ture of the acts it performs. NERVII, a powerful and warlike people of the ancient Gallia Belgica, whose territory stretched from the Sambre to the ocean, not subdued by Casar without an obstinate resistance. NERVOUS DISEASES, diseases due either to actual changes in the struc- ture of nerve-fibers or nerve-centers, or to some irregularity of nerve function without actual structural change. Thus nervous diseases may be due to in- flammation or degeneration of nerve substance; to the pressure on some part of the nervous system of tumors, ef- fused blood, or other fluid; to the death of some part by the cutting off of its blood supply, etc.; or may be the re- sult of lowered nervous action as a part of general bad health. NESS, LOCH, a long, narrow lake of Inverness-shire, the second largest in Scotland, 6% miles S. W. of Inverness; 50 feet above sea-level ; length N. N. E. 22*/^ miles; average breadth 1 mile; area 19 square miles. It receives the Morriston, Oich, Foyers, and other streams, and sends off the river Nesa