'////; /'/;/,'/////; /v.i/. .\7-;/,mrx .STXV/.M/ 



The nerves of the pia mater are prol.ably all fur the supply of the numerous Mood -, 

 in il. They areompaiiy the vessels anil I'orni ienninal, | cri\aseiilar |i|e\iise> al.oiit them. I liey 

 are cliiellv sympathetic, \asn-inotor In the smooth muscle in the walls of the vessels. .\ few 

 fibres .l i ereliro-spinal origin occur, all of whleh are, no d.mlit. of the sensory variety. 'I'hc 

 nerve .supply of the spinal pia mater is derived from the reeurrent branches ol il.e spinal ne: 



THE I'KIMPIIKUAL NERVOUS SYSTEM 



Tl> intimate connect ion and consequent control exercised by the central nervous 

 system over :ill tlie I issues and organs of the body is attained through the peripheral 

 nervous s.ystem. This system, abundant ly attached to the central system, consists 

 of numerous bundles of nerve-fibres which divide and ramify throughout (he body, 

 anastomosing with each other and forming various plexuses, large and small. The 

 terminal rami divide and subdivide until the division attains the individual nerve- 

 fibres of which (hey are composed, and finally the nerve-fibres terminate in relations 

 with their allotted peripheral elements. It is by means of this system that stimuli 

 arising in the peripheral tissues are conveyed to the central system, and that im- 

 pulses in response are borne from the central system to the peripheral organs. For 

 purposes of description, as well as upon the basis of certain differences in structure, 

 arrangement, and distribution, the peripheral nervous system is separated into two 

 main divisions; <|) the cerebro-spinal and (2) the sympathetic system. 



Both of these divisions include numerous ganglia or peripheral groups of nerve- 

 cells from which arise a considerable proportion of the fibres forming their nerve- 

 trunks, but neither of the divisions may be considered wholly apart from the central 

 system nor are they separate from each other. The sensory or afferent fibres of the 

 cerebro-spinal nerves pass by way of the afferent nerve-roots into the central system 

 and contribute appreciably to its bulk, and the motor or efferent fibres of these nerves 

 have their cells of origin (nuclei) situated within the confines of the central system. 

 The sympathetic system is intimately associated with the cerebro-spinal, and conse- 

 quently with the central system (1) by means of fibres which enter the cerebro- 

 spinal ganglia and convey impulses which enter the central system; (2) by efferent 

 fibres of central origin which course in the nerve-trunks and terminate in the ganglia 

 of the sympathetic system; (3) also, the sympathetic trunks usually contain numer- 

 ous afferent cerebro-spinal fibres which thus course to their peripheral termination, 

 usually in the so-called 'splanchnic area,' or domain of the sympathetic, in company 

 with the sympathetic fibres. Likewise the peripheral branches of the cerebro-spinal 

 nerves often carry for varying distances numerous sympathetic fibres which are on 

 their way to terminate either in other sympathetic ganglia or upon their allotted 

 tissue-elements. 



The following differences between the cerebro-spinal and sympathetic systems 

 of nerves may be cited: (1) The cerebro-spinal nerves are anatomically continuous 

 with the brain and spinal cord; probably no fibres arising in the sympathetic ganglia 

 actually enter the central system. (2) The ganglia of the cerebro-spinal nerves all 

 lie quite near t he central axis, in line on either side of it, and at more or less regular 

 intervals; the sympathetic ganglia are scattered throughout the body tissues, are 

 far more numerous and more variable in size, and probably only the larger of them 

 are symmetrical for the two sides of the body. (3) The "cerebro-spinal nerves are 

 paired throughout, and the nerves of each pair are symmetrical as to their origin and 

 also, with certain exceptions (notably the vagus), 'in their course and distribution; 

 nrostof the larger and more proximal of the sympathetic nerve-trunks are symmetrical 

 for the two sides of the body; many of them are not, and many of the smaller and 

 most of the more peripheral nerves are not pairedatall. (4) Kven in their finer twisrs. 

 the cerebro-spinal nerves of the two sides probably do not anastomose with each 

 other across the mid-line of the body; the sympathetic nerves do so abundantly, 

 especially within the body cavity. (5) The eerebro-spinal nerves are distributed to 

 the ordinary sensory surfaces of the body and the organs of special sense and to the 

 somatic, striated or -voluntary' muscles of the body: the sympathetic fibres are de- 

 voted chiefly to the supply of the so-called involuntarv muscles of the body, including 

 the smooth muscle in the walls of the viscera and in the walls of the blood and lymph 



