CHAP. VII.] 



THE NERVOUS SYSTEM. 



77 



Connective tissue also surrounds these bundles in the form of a 

 sheath. The smaller nerves may consist of a single funiculus; 

 but the larger nerve-trunks contain several funiculi united by 

 connective tissue and surrounded by a common sheath of the 

 same material. 



Although the nerves branch frequently throughout their 

 course, and these branches often meet and fuse with one 

 another, or with the branches of other nerves, yet each nerve - 

 fibre always remains quite distinct, never branching until it 

 reaches its termination, and never uniting with other nerve- 

 fibres. The nerve-trunk is thus merely an association of indi- 

 vidual fibres which proceed together towards the periphery. 

 At any time one or more indi- 

 vidual fibres may leave the 

 main body and pass to their 

 terminations, or may join an- 

 other nerve; but in any case 

 each fibre always remains per- 

 fectly distinct. 



Physiologically speaking, 

 nerve-fibres are of two kinds, 

 those which normally transmit 

 impulses from the central ner- 

 vous system to the periphery 

 (the efferent or motor fibres), 

 and those which normally 

 transmit impulses in the re- 

 verse direction (the afferent or 



sensory fibres). Hence nerves are spoken of as motor, sensory, 

 or mixed ; according as they contain motor (efferent), sensory 

 (afferent), or both kinds of fibres. 



The cell-bodies, from which the axones of the peripheral 

 nerve-fibres arise, are not scattered promiscuously throughout 

 the body, but are gathered together in certain definite regions 

 or groups. These form the gray matter of the cerebro-spinal 

 axis and the ganglia. 



The ganglia. A ganglion is a small collection of cell-bodies 

 connected by means of nerve-fibres (axones or dendrones) with 

 other ganglia, and with the central nervous system. The 

 ganglia may be divided into two large classes, the spinal and 



FIG. 05. NERVE-FIBRES, u, i^i\e- 

 fibre, showing complete interruption of 

 the white substance ; 6, another nerve- 

 fibre with nucleus. In both these nerve- 

 fibres the white substance is stained black 

 with osmic acid, and the axoue is seen run- 

 ning as an uninterrupted strand through 

 the centre of fibre, c, ordinary nerve- 

 fibre unstained ; d, e, smaller nerve-fibre; 

 /, varicose nerve-fibre ; g, non-medullated 

 nerve-fibres. 



