358 . SPECIAL ANATOMY. 



between and round about the primitive nervous fibres. Their ex- 

 ternal vaginal processes give a weak, gray appearance (especially 

 to the n. sympathicus\ misled by which they have been regarded 

 as vegetative, organic, nervous fibres, since they stand in relation 

 with forms of uniting tissue, only (Valentin). 



The ganglion globules of the central portions are extremely deli- 

 cate and difficult to isolate; the vaginal formation is here, also, 

 doubtful. They form the gray, yellow, and brown substance of 

 the brain and spinal marrow. 



The white or medullary substance is formed of primitive fibres. 

 The gray or cortical substance of ganglion globules ; it is more 

 plentifully supplied with vessels than the white. 



610. 2. The chemical elements. 



The medullary substance of the brain consists of four-fifths water; 

 Cholesterine ; Cerebric acid, free, or united with soda or phosphate 

 of lime; Oleophosphoric acid, free, and with soda; Oleine and Mar- 

 garine; Oleic and Margaric acids; Albumen, with sulphur (Fremy). 

 Moreover, the sheaths of the nerves, with vessels and uniting tissue, 

 are to be attended to in the examination. The medullary substance 

 contains more fat, the cortical substance more albumen, the spinal 

 marrow more fat and less albumen, the nerves more albumen than 

 the brain. (Vauquelin). 



611. The peripheral portion of tlue Nervous system^ 



nerves, nervi, are long portions formed of bundles (fasciculi), lying 

 close together, and cords (funiculi) of primitive fibres, which place 

 the surfaces of the body and muscles in connexion with the central 

 portions, and are, partly, the conductors of sensations from the 

 periphery to the centre ; partly, the conductors of movements from 

 the latter to the former. There are two kinds, white and gray : 



The white nerves (animal or cerebro-spinal) are strong, bright, 

 transversely striped, spread out in the muscles of the trunk and in 

 the skin, and are surrounded by a sheath of strong, fibrous, uniting 

 tissue, the Neurilemma, which blends, externally, with the amor- 

 phous uniting tissue of the surrounding parts ; internally, in the 

 outer sheath of the delicate nervous fasciculi (see before). The 

 primitive fibres of the white nerves (diam. 0-080 0-084 of a line) 

 are strongest in the muscles of voluntary motion, and most delicate 

 in the nerves of the senses. 



The gray nerves (vegetative) are soft (see nervi molles), but 

 tolerably strong, diaphanous, reddish gray, not transversely striped ; 

 their neurilemma very strong, and provided with an annular layer. 



