906 



THE NERVOUS SYSTEM 



line of the body, it turns sharply outwards and sends rami medianwards and lateral- 

 wards to supply the skin of the ventral aspect of the body. In the region of the 

 limb* the typical arrangement is interfered with in that what corresponds to the lateral 

 and anterior branches of the division are carried out into the limbs for the skin and 

 muscles there, instead of supplying the lateral and ventral parts of the body-wall. 



Nerve-fibres arising in the spinal ganglion and fibres from the ventral or motor 

 root pass directly from the nerve-trunk into the anterior primary division of the 

 spinal nerve. This division also receives sympathetic nerve-fibres by way of the 

 ramus communicans. These latter accompany the division and are distributed to 

 their allotted elements in the territory it supplies. 



The rami communicantes are small, short, thread-like branches by which the 

 nerve-trunks are connected with the nearest ganglion of the vertically running 

 gangliated cord of the sympathetic (sympathetic trunk). The trunk or an- 

 terior primary division of every spinal nerve has at least one of these; most 



FIG 673 DIAGRAM ILLUSTRATING THE OHIGIN OF THE COMPONENT NERVE-FIBRES OF THE 



PRIMARY DIVISIONS OF A TYPICAL SPINAL NERVE. 

 AS, Afferent sympathetic fibre; D, Dogiel spinal ganglion-cell of type II. 



DORSAL ROOT 



GREY RAMUS 

 COMMUNICANT 



WHITE /.M.vr.v 

 COMMUNICANS 



SYJfPATBSTlC} 



ANGLION GASGLI . 

 I ATKlJ 



SYMPATHETIC C ORD 



TRUNK 



POSTERIOR PRI- 

 MARY DIVISION 



ANTEIH/U: 1'Rl- 

 MARY DIVISION 



AFFKRF.XT SPLAS- 

 rn\-rr FIRHF, 



EFFF.KF.XTHrI.AS- 



CHKIC FIBRE 

 " N GREY KASII-H 



COM.VUX IVANS 

 WHITE R.I M!'S 

 COMMTNtCANS 



SK.\\fH TO ritK 



SYMPATHETIC 



of the nerves have two, and sometimes there are three. The nerves of the 

 cervical region usually have but one, and this is composed largely of sympathetic 

 fibres (grey ramus). Where *here are two, one usually contains medullated fibres 

 sufficient to give it a whiter appearance (white ramus). In the upper cervical 

 and in the sacral regions one sympathetic ganglion may be connected with two 

 or more spinal nerves, and sometimes one nerve is connected with two ganglia. 

 The rami communicantes of the spinal nerves are equivalent to the communicating 

 rami connecting certain of the cranial nerves with the sympathetic system (tri- 

 geminus, glosso-pharyngeus, vagus). The medullated fibres of the rami and, there- 

 fore, the white rami consist chiefly of fibres from the spinal nerves, viz., fibres from 

 the spinal ganglion-cells which enter and course to their distribution through the 

 sympathetic nerves, splanchnic afferent fibres, and fibres from the ventral roots 

 of the spinal nerves which terminate in the sympathetic ganglia, splanchnic efferent 



