24 THE INVOL UNTAR Y NER VO US S YSTEM 



mass of nervous material, and so enabled a more efficient con- 

 centration of the elements of the voluntary nervous system. 

 At the same time the involuntary connector fibres, which form 

 the efferent part of the rami communicantes, were sufficient 

 to maintain the necessary efficiency of the interaction be- 

 tween the central nervous system and the motor cells of the 

 involuntary system, taking into consideration the nature of 

 the movements of involuntary muscle. These movements are 

 essentially movements en masse and not delicately co-ordinated 

 movements, such as are so characteristic of the voluntary system ; 

 indeed, the evidence shows that movements of the involuntary 

 system of muscles, brought about reflexly through the central 

 nervous system, always involve a large number of muscle fibres. 

 This must be the case when we consider that each single fibre 

 that leaves the central nervous system can activate by means of 

 collaterals many motor nerve cells, each of which in its turn in- 

 nervates many muscle fibres. 



The limits of the outflow of nerves from the spinal cord, 

 which pass to the cells of the sympathetic ganglia (Fig. 4), are 

 defined by the structure of the anterior roots and consequent 

 presence or absence of a white ramus communicans. The upper 

 limit is defined by the brachial plexus and the lower by the 

 lumbo-sacral plexus. 



The next question for consideration was whether there were 

 similar outflows of fine medullated efferent fibres either below or 

 above these limits. To settle this question I proceeded to cut 

 sections of the anterior roots of all the spinal nerves, and found 

 that again in the anterior roots of the second and third sacral 

 nerves there was evidently another mass of these small medullated 

 fibres. It was easy to follow these small fibres outwards into two 

 separate nerves which joined together to form the nervus erigens ; 

 that is to say, the structure of these roots demonstrates an 

 outflow of fine medullated fibres from the spinal cord, to 

 form a ramus communicans, not to any ganglia of the verte- 

 bral chain, but to separate sets of ganglia lying on the surface 

 of the bladder and rectum (Fig. 5, P). These fibres pass 

 directly to these ganglion cells without having anything to 

 do with the lateral or main chain of sympathetic ganglia, just 

 as the nerves, which form the splanchnics, pass direct to the 

 collateral ganglia of the sympathetic independently of the lateral 



