INTRODUCTION 3 



the ventral roots, for the cells of the sympathetic system arc entirely 

 efferent in nature, not afferent ; therefore, the fibres entering into them 

 from the central nervous system leave the spinal cord by ventral, not 

 dorsal roots. 



Following out this clue, I then found that in addition to this 

 thoracico-lumbar outflow of efferent ganglionated visceral nerves, 

 there are similar outflows in the cranial and sacral regions, belong- 

 ing in the former case especially to the vagus system of nerves, and 

 in the latter to the system of nerves which pass from the sacral 

 region of the cord to the ganglion-cells of the hypogastric plexus, 

 and from them supply the bladder, rectum, etc. To this system of 

 nerves, formerly called the nervi erigcntes, I gave the name pelvic 

 splanchnics, in order to show their uniformity with the abdominal 

 splanchnics. These investigations led to the conclusion that the 

 organic system of nerves, characterized by the possession of efferent 

 nerve- cells situated peripherally, arises from the central nervous 

 system by three distinct outflows — cranial, thoracico-lumbar, and 

 sacral, respectively. To this system Langley has lately given the 

 name ' autonomic' These three outflows are separated by two gaps 

 just where the plexuses for the anterior and posterior extremities 

 come in. 



This peculiar arrangement of the white rami communicantes set 

 me thinking, for the gaps corresponded to an increase of somatic 

 musculature to form the muscles of the fore and hind limbs, so that 

 if, as seemed probable, the white rami communicantes arise segmentally 

 from the spinal cord, then a marked distinction must exist in 

 structure between the spinal cord in the thoracic region, where the 

 visceral efferent nerves are large in amount and the body muscu- 

 lature scanty, and in the cervical or lumbar swellings, where the 

 somatic musculature abounds, and the white rami communicantes 

 scarcely exist. 



I therefore directed my attention in the next place to the 

 structure of the central nervous system in the endeavour to asso- 

 ciate the topographical arrangement of cell-groups in this system 

 with the outflow of the different kinds of nerve-fibres to the 

 peripheral organs. 



This investigation forcibly impressed upon my mind the 

 uniformity in the arrangement of the central nervous system as far 

 as the centres of origin of all the segmental nerves are concerned, 



