1118 



GENERAL ANATOMY OR HISTOLOGY. 



Chemical Composition. The amount of water in nervous tissue varies with the 

 situation. Thus in the gray matter of the cerebrum it constitutes about 83 per 

 cent., in the white matter from the same region about 70 per cent., ^rhile in the 

 peripheral nerves, such as the sciatic, it may fall to 60 per cent. The solids con- 

 sist of proteids (in the gray matter they form half the total solids), ne-urokeratin, 

 nuclein, protagon, lecithin, cerebrosides, cholesterin, nitrogenous extractives, and 

 salts, with some gelatin and fat from the adherent connective tissue. 



The nervous structures are divided, as before mentioned, into two great systems, 

 viz., the cerebro-spinal, comprising the brain and spinal cord, the nerves con- 

 nected with these structures, and the ganglia situated on them ; and the sympa- 

 thetic, consisting of a double chain of ganglia and the nerves connected with them. 

 All these structures require separate consideration ; they are composed of the two 



kinds of nervous tissue above described, 

 intermingled in various proportions, and 

 having, in some parts, a very intricate 

 arrangement. 



The brain or encephalon is that part 

 of the cerebro-spinal system which is 

 contained in the cavity of the skull. It 

 is divided into several parts, which will 

 be described in the sequel. In these 

 parts the gray or vesicular nervous 

 matter is found partly on the surface 

 of the brain, forming the convolutions 

 of the cerebrum and the laminae of'the 

 cerebellum. Again, gray matter is 

 found in the interior of the brain, col- 

 lected into large and distinct masses or 

 ganglionic bodies, such as the corpus 

 striatum, optic thalamus, and corpora 

 quadrigemina. Finally, gray matter is 

 found intermingled intimately with the 

 white, but without definite arrangement, 



FIG. 656. Transverse section through a microscopic 

 ntrve, representing a compound nerve-bundle, sur- 

 rounded by perineurium. Magnified 1'20 diameters. 

 The meduflated fibres are seen as circles with a cen- 

 tral dot viz., medullary sheath and axis-cylinder in 

 transverse section. They are embedded in endoneur- 

 ium, containing numerous nuclei, which belong to the 

 connective-tissue cells of the latter. (Klein and Noble 

 Smith. ;> p. Perinenrmm, consisting of laminae of fibrous 

 connective-tissues, alternating with flattened nucleated 

 connective-tissue cells. 1. Lymph-space between epi- 

 neurium and surface of nerve-bundle. 



as n the gray matter in the pons 

 Varolii and the floor of the fourth 

 ventricle. 



The white matter of the brain is 

 divisible into three distinct classes of 



fibres : (1) Diverging or peduncular 



fibres, which connect the hemispheres with the medulla oblongata and the spinal 

 cord. (2) Commissural fibres, which connect together the two hemispheres. (3) 

 Association fibres, which connect different parts of the same hemisphere. 



The manner in which these fibres are intermingled with each other and with 

 the gray matter in the brain and spinal cord is very intricate, and can be fully under- 

 stood only by a careful study of the details of its descriptive anatomy in the sequel. 

 The further consideration of this subject will therefore be deferred until after the 

 description of the various divisions of which the cerebro-spinal system is made up. 



The nerves are round or flattened cords, formed of the nerve-fibres already 

 described. They are connected at one end with the cerebro-spinal centre or with 

 the ganglia, and are distributed at the other end to the various textures of the 

 body ; they are subdivided into two great classes the cerebro-spinal, which pro- 

 ceed from the cerebro-spinal axis, and the sympathetic or ganglionic nerves, which 

 proceed from the ganglia of the sympathetic. The cerebro-spinal nerves consist 

 of numerous nerve-fibres collected together and enclosed in a membranous sheath 

 (Fig. 656). A small bundle of primitive fibres, enclosed in a tubular sheath, is 

 called a funiculus ; if the nerve is of small size, it may consist only of a single 

 funiculus ; but if large, the furiiculi are collected together into larger bundles or 



