632 Mr. Walter H. Gaskell [June 4, 



cerebro-spinal system, because these fibres all pass out of the nerve- 

 roots before they reach the spinal cord. 



2. White or medullated nerve-fibres constitute the only link 

 between the sympathetic and cerebro-spinal systems, constituting the 

 white rami communicantes. 



3. Consequently the connection between these two nervous 

 systems is limited to the region of white rami communicantes, i. e. to 

 the region between the second thoracic and second lumbar nerves. 



Fui'ther, these conclusions are borne out when we attempt to 

 follow the white rami communicantes into the central spinal axis by 

 means of their structural peculiarities ; sections of osmic preparations 

 show that each white ramus is composed chiefly of very small 

 medullated nerve fibres, varying in size from 1*8 /x to 3*6 ya, very 

 much smaller, therefore, than the large medullated nerves which form 

 the bulk of the anterior roots of the spinal nerves, these latter varying 

 between 14 ^ to 20 /x or even larger. Clearly then the fibres of the 

 white ramus communicans ought to show very conspicuously among 

 the large fibres of the anterior roots whenever they are present in those 

 roots. I have cut sections of the anterior roots of all the spinal nerves 

 in the dog, and have found, as I show you on this screen, that these very 

 fine medullated nerve-fibres make their appearance for the first time 

 in the anterior roots of the second thoracic nerve ; they are found in 

 large quantities in all the anterior roots between the second thoracic 

 and second lumbar, and then again the anterior roots immediately 

 below the second lumbar are free from such groups of very fine fibres. 

 We see then that exactly corresponding to the presence of white rami 

 communicantes in the thoracic region we find groups of characteristic 

 fine medullated fibres existing in the anterior roots, fibres which 

 clearly form part of the white ramus communicans, and confirm by 

 their presence the conclusion already arrived at, viz. that the nerves 

 which pass from the spinal cord into the sympathetic system are 

 limited to the thoracic region of the cord. 



We can now go a step further and argue in the reverse direction 

 that the presence of groups of these very fine medullated fibres in 

 the anterior roots of any nerve implies the existence of nerve-fibres 

 belonging to the same system as the white rami communicantes or 

 rami viscerales as we may now call them. Examination shows how 

 just is this argument, for I find that the same groups of fine nerve- 

 fibres suddenly appear again in the anterior roots of the second and 

 third sacral nerves, and can be traced into that well-known nerve 

 which passes from the second and third sacral nerves into the hypo- 

 gastric plexus to supply the rectum, bladder, and reproductive organs ; 

 a nerve, therefore, which may be looked upon as the white ramus 

 communicans of the sympathetic ganglia which form the hypogastric 

 plexus. 



Again, in the cervical region, although such groups of fine fibres 

 are absent from the anterior roots of all the cervical nerves, yet they 

 form a conspicuous part of the upper roots of the spinal accessory 



