1886.] on the Sympathetic Nervous System. 531 



muscular tissue rather than to any action of nerve-cells comparable 

 to the nerve-centres of the spinal cord ; I shall deal entirely with the 

 anatomical argument and show you step by step how the nerve-iibres 

 which constitute the symj^athetic system can be traced to their origin 

 in the central cerebro-spinal axis. 



Evidently, in endeavouring to determine by anatomical means 

 whether the sympathetic and cerebro-spinal systems are in reality 

 independent of one another, our attention must necessarily be 

 especially concentrated upon the nature of the connecting link be- 

 tween the two systems, i. e. upon the nature of the rami communi- 

 cantes. Largely owing to the preconceived notions of anatomists, 

 you will find that the rami communicantes are arranged symmetrically 

 in connection with all the spinal nerves of the body. In reality this 

 is far from being the case, the rami communicantes of the thoracic 

 nerves differ from those above them, i. e. of the cervical nerves, and 

 from those below them, i. e. of the lumbar nerves, in two important 

 particulars : in the first place the corresponding sympathetic ganglion 

 is connected with each thoracic nerve by two rami communicantes ; 

 and secondly, these two rami differ in colour, one being grey, i. e. 

 composed almost entirely of non-medullated nerves, and the other 

 white, i. e. composed essentially of medullated nerve-fibres. 



This double nature of the ramus communicans is confined to the 

 region lying between the two large plexuses which supply the anterior 

 and posterior extremities, viz. the brachial, lumbar, and sciatic 

 plexuses; the rami communicantes to the lower cervical and first 

 thoracic nerves, as well as those to the nerves forming the anterior 

 crural and the sciatic, are, on the other hand, single, and are composed 

 only of grey rami. In other words, the sympathetic chain is con- 

 nected with the central nervous system by means of white rami com- 

 municantes only between the second thoracic and second lumbar 

 nerves. 



Further, I have been able to trace both the white and grey rami 

 in their journey to the spinal cord by means of consecutive sections 

 of osmic acid preparations, and have found that the grey rami pass 

 out of the sympathetic ganglion as a single nerve, and then ramify in 

 the connective tissue about the vertebral foramina, a portion only 

 reaching the spinal nerve-trunk ; the grey fibres of this portion pass 

 mainly along the nerve peripherally, the few which pass centrally 

 never reach the spinal cord, but pass out with the connective tissue 

 which lies in between the medullated nerve-fibres of the anterior and 

 posterior roots, to ramify over and to supply the blood-vessels of the 

 various membranes which inclose the spinal cord. 



In fact the grey rami communicantes are peripheral nerves, which 

 partly supply the vertebrae and the membranes of the cord, and partly 

 pass to their destination in the same direction as the efferent fibres 

 of the spinal nerve itself. 



So far then I come to these conclusions : 



1. The sympathetic does not send non-medullated fibres into the 



