HUMAN PHYSIOLOGY. 



but also of fetid effete matters removed from the 

 system by the lower bowel. 



II. THE FUNCTION OF INNERVATION. 



The vital processes included under the function 

 of nutrition belong to the class of functions known 

 as vegetative, because certain of them are common 

 to vegetables as well as to animals. These func- 

 tions have as their object the preservation of the 

 plant. The animal has, however, another set of 

 organs, by the use of which it becomes conscious 

 of a world external to itself. By means of certain 

 functions, which, from their occurrence in animals 



d 



Fig. 7. Human Adult Brain : 



a, anterior lobe of cerebrum ; b, middle lobe ; c, posterior lobe of 

 cerebrum, appearing behind : d, cere bellar hemisphere ; e, medulla 

 oblongata ; f, fissure of Sylvius ; g, longitudinal fissure ; A, h, 

 olfactory bulbs ; i, optic commissure the optic nerves are seen 

 interchanging fibres ; /, three roots of olfactory process ; m, white 

 round bodies (corpora albicantia) , the terminations of the anterior 

 portions of tornix ; , where the vessels perforate the brain sub- 

 stance, hence called posterior perforated space ; o, third pair of 

 nerves coming to supply muscles of the eyeoall, from/, the crus 

 cerebri ; g, fourth nerve, turning round from the valve of Vieu- 

 sens ; r, fifth pair ; s, pons varolii ; i, sixth pair of nerves ; u, 

 seventh pair, portio dura for muscles of face, and portio mollis 

 for hearing ; v, posterior pyramids of cerebellum, seen to inter- 

 change fibres ; w, and two below, are eighth pair viz. glosso-pha- 

 ryngeal, vagus or pneumo-gastric, and spinal accessory nerve ; 

 between w and v is the small prominence called olivary body ; 

 x, y, two roots of ninth pair of nerves, motor nerve of tongue. 



only, are termed animal, all the higher creatures, 

 and especially man, are endowed with Sensation, 

 Motion, and Volition. These powers are due to 

 the presence of a Nervous System, including two 

 sets of nerves and nerve - centres namely, the 

 cerebro-spinal system and the sympathetic system. 



The former consists of the cerebro-spinal axis, 

 composed of the brain and spinal cord, and the 

 cerebral and spinal nerves connected with this 

 axis ; while the latter consists chiefly of a double 

 chain of ganglia or nervous masses, lying at the 

 sides of the spinal column, and united with one 

 another and with the spinal nerves by connecting 



threads of nervous tissue. The sympathetic 

 system influences the heart and blood-vessels, and 

 the intestines. It has the power of stimulating 

 the action of the heart by acting on ganglia in 

 its substance. It maintains the blood-vessels in 

 a certain state of contraction. 



The cerebro-spinal axis lies protected in the 

 cavity of the skull and spinal column, and is 

 covered by three membranes, which serve for 

 protection and for the supply of blood. 



Nerve-matter is of two kinds, white and gray, 

 and may be readily seen by cutting through the 

 brain of a sheep or of any other animal, when it 

 will be observed that there is an outer layer of 

 gray matter, while the interior is white. In the 

 spinal cord these relations are reversed, the gray 

 matter lying in the centre. The nerves consist 

 entirely of the white tissue. The microscope 

 shews that the gray matter is made up of round, 

 oval, or star-like cells with a nucleus, and sending 

 off prolongations, which either unite with those of 

 other similar cells, or are continued as nerve-tubes. 

 These cells, termed nerve-cells, vary much in size, 

 from the TiAnrth to the rUth of an inch. The 

 white matter consists of tubes, transparent as glass 

 when examined alive ; but immediately after 

 death, shewing two well-defined lines on each side 

 of a broad clear space. They thus appear to con- 

 sist of two parts a central part, which probably 

 conducts the nervous influence, surrounded by a 

 substance, of different chemical constitution, which 

 may act as an insulator of the nervous force. A 

 nerve consists of many of these tubes running 

 alongside of each other, and here and there 

 plexuses are formed by certain tubes diverging and 

 running from one nerve to another. The function 

 of the nerve-tube is to receive an impression of 

 any kind, mechanical, chemical, thermal, or voli- 

 tional, thereupon to generate an influence, and to 

 conduct this influence to or from a nerve-centre. 

 The rapidity of the nerve-current is from 75 to 120 

 feet per second ; incomparably slower than light, or 

 electricity. The nerve-cells either receive or orig- 

 inate nervous force. 



The brain consists of the cerebrum, or brain 

 proper, which occupies the whole of the upper and 

 front parts of the cavity of the skull ; the cerebellum, 

 or little brain, lying beneath the hinder part of the 

 cerebrum ; and the medulla oblongata, or oblong 

 marrow, which may be regarded as a continuation 

 of the spinal cord within the cavity of the cranium, 

 and as forming the connection between the brain 

 and cord. The cerebrum and cerebellum are 

 almost completely bisected into two lateral halves 

 by a deep longitudinal fissure ; and the surface of 

 the former is divided by a considerable number of 

 tortuous furrows, nearly an inch deep, into convo- 

 lutions. As the gray matter is extended into these 

 furrows, its quantity is thus vastly increased. 



At the base of the cerebrum, and connected 

 with it, there are two large ganglionic masses of 

 gray and white matter, called the. corpora striata; 

 behind these, other two bodies of a similar nature, 

 the optic thalami; and still farther back, four bodies, 

 two on each side, the corpora quadrigemina. All 

 these parts of the brain are connected with each 

 other by numerous tubes. The tubes from the 

 spinal cord pass upwards in the medulla oblongata ; 

 those from the posterior part of the cord going 

 chiefly to the cerebellum, while those from the 

 anterior pass to the cerebrum. In the cerebrum, 



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