II. Organs. 4. Nervous System. 



17 



4. Nervous System. 



Ganglion cells and nerve-fibres are usually aggregated, the 

 groups of ganglion cells are known as ganglia, the bundles of 

 nerve-fibres as nerves. It generally happens that most of the 

 ganglia are connected to form a central nervous system, 

 from which spring 



the nerves supplying .^ , . sa 



muscles, sense organs, 

 and so on, all these 

 nerves are included 

 in the peripheral 

 nervous system; 

 nerve fibres are, of 

 course, present also 

 in the central nervous 

 system, and especially 

 in the strands con- 

 necting the ganglia. 

 Similarly the ganglia 

 do not occur exclu- 

 sively in the central 

 nervous system, al- 

 though they are con- 

 nected with it, even 

 when situated in 

 remote parts of the 

 body. 



Nerves are called 

 motor or sensory, 

 consisting respec- 

 tively of motor or 



sensory fibres*; many i,- i, -n- t ^ w i- 



■' ■ 1 -^'B- '-'■ Diagram of a nervous system, eg — eg ganglia 



are, however, mixed, of the central nervous system, I— I" and t—t'" longitudinal 



and contain both kinds and transverse connective fibres, sa sensory cells, s nerve 

 fibres, springing from them, g peripheral ganglion, each 



of fibres. Nerves of whose cells gives off two fibres, one branching in the 



USUallvbranch during epidermis ey, the others going to eg. s" sensory fibre, 



•^ . . .^. which arises in cells lying in eg, and branches in ep'. 



their course, dividing 6 motor fibre, which goes to a muscle m.— Orig. 



gradually into thin- 

 ner and thinner strands, consisting of fewer and fewer fibres. 



The central nervous system is, as it were, the " Exchange" of the 

 body; by the motor nerves it transmits impulses to the muscular 

 elements and thus controls their movements ; by the sensory nerves 

 it receives impressions sent from the different sense organs. 



* Sensory nerves are further classified as nerves of touch, taste, smell, hearing, or 

 sight. 



