468 THE KffRVOUS SYSTEM 



ally transmitting cellulipetal impulses, and the neuraxes and col- 

 laterals, which transmit cellulifugal impulses. The cell body or 

 nerve cell has already been sufficiently described.* 



The dendrite is a broad arborizing process whose substance 

 closely resembles the cytoplasm of the cell body in its microscop- 

 ical appearance and in its staining reactions. It branches freely, 

 but always dicotymously, and usually ends at a point not very 

 remote from its cell body. 



The neuraxis (nerve fibre, axis cylinder process, axon, dendron, 

 neurite, etc.) is a long and slender process. It arises either directly 

 from the cell body or indirectly from the trunk of one of its den- 

 drites. It gives off numerous collaterals at right angles to the 

 parent fibre throughout the greater part of its course, and finally 

 terminates, as do also its collaterals, in an end brush (terminal 

 arborization, felt work, basket work, etc.), or in one of the several 

 forms of peripheral nerve end organs, 



The end brushes are apparently formed by the rapid separation 

 of the fibre into its component fibrillae. 



The neuraxis is usually a much longer process than are the 

 dendrites. Unlike the latter, it extends not merely to other por- 

 tions of the grey " nucleus" in which its cell body lies, but fre- 

 quently it passes without interruption of its anatomical continuity 

 to other and even very distant parts. The wide radius through 

 which these fibres are distributed is well illustrated by the passage 

 of neuraxes, coming from nerve cells of the cerebral cortex, to the 

 grey matter of the spinal cord ; other nerve cells in the spinal cord 

 send their neuraxes through the entire length of the spinal nerve, 

 to supply even the most remote tissues of the body. While, there- 

 fore, the cell bodies and dendrites are measured in millimetres or 

 micromillimetres, the neuraxis is often to be measured only in 

 centimetres and decimetres. There are very few cells in the body 

 which are in any way comparable to the nerve cell or neurone for 

 the large size of its cell body and the extensive area of distribu- 

 tion of its processes. 



All portions of the neurone, its neuraxis and collaterals as well 

 as its dendrites, are dependent upon the cell body for nutrition ; 

 hence each nerve cell becomes the so-called trophic center for all 

 of its processes. 



The entire nervous system may be considered as an enormous 

 tangle, formed by the interlacing processes of an innumerable 



* Chapter VIII. 



