NERVOUS TISSUES 31 



peripheral distribution of both afferent and efferent fibres, there is 

 a marked difference between those associated with the external or 

 somatic portions of the body and providing for external adjust- 

 ments to the environment and those connected with internal or 

 visceral portions and serving for the internal integration of processes 

 within the body. Consequently somatic and visceral kinds of both 

 afferent and efferent fibres are distinguished. 



cgv 



Fig. 18. Photomicrograph of transverse section of the spinal 

 cord of a rabbit. X 15. The central canal is visible in the middle 

 of the picture, cgd, dorsal column (horn) of grey matter; cgv, 

 ventral column (horn) of grey matter; fd, dorsal funiculus of the 

 white matter; fl, lateral funiculus of the white matter; fmv, 

 ventral median fissure; fv, ventral funiculus of the white matter; 

 rd, dorsal root of spinal nerve; rv, position of ventral root of 

 spinal nerve; smd, dorsal median sulcus. 



Nerve fibres differ among themselves in such properties as 

 calibre, thickness of the sheaths, and reaction to certain stains and 

 it has been possible to associate some of these differences with the 

 conduction of certain specific kinds of impulses. 



While the nerve-cell bodies mostly lie within the central nervous 

 organs, some are in the peripheral nerves. The majority of the 

 latter are grouped into definite masses, each of which is called a 

 ganglion. 



On account of the difference in colour produced by the presence 

 or absence of myelin, the cellular and the myelinated fibrous 



