202 THE AUTONOMIC NERVOUS SYSTEM [CH. XVII. 



to the involuntary muscular tissue and glands in the body walls and 

 skin. 



Thus in the lateral chain of ganglia we find the cells on the 

 course of the pilo-motor nerves, of the nerves to the sweat glands, 

 possibly of the splenic nerves, and last but not least, of the vaso- 

 constrictors of the head, limbs, and body wall. Indeed, at one time, 

 Gaskell suggested that the lateral chain should be called the chain of 

 vaso-motor ganglia. In general terms the cell-stations are situated 

 in ganglia that correspond with the various spinal segments ; those 

 for the lower limbs, for instance, being further down the chain than 

 those for the trunk and upper limb. The vaso -constrictor fibres 

 destined for the head, ascend the cervical sympathetic and do not 

 reach their cell-station until they arrive at the superior cervical 

 ganglion. 



(b) The pre-ganglionic fibres traverse the lateral ganglia, and 

 emerge still as pre-ganglionic fibres, which find their cell-stations in 

 more or less outlying ganglia (collateral or terminal). We have 

 already taken the splanchnic nerve as one example of this mode of 

 distribution ; the nerve contains inter alia the vaso-constrictor fibres, 

 and viscero-inhibitory fibres of the abdominal organs. The hypo- 

 gastric nerve arises in a similar way from the inferior mesenteric 

 ganglion and joins the pelvic plexus. The medullated pre- 

 ganglionic fibres of this nerve arise from the upper lumbar nerve- 

 roots. 



4. The autonomic nerve-fibres which arise from the sacral region of 

 the spinal cord. The pre-ganglionic fibres emerge in the white rami 

 of the second, third, and fourth sacral nerves. They pass through 

 the sacral ganglia of the lateral chain without forming connections 

 with any cells there, and they pass on as the nervus erigens, or pelvic 

 nerve, to join the pelvic plexus. The fibres of this nerve supply vaso- 

 dilator fibres to the external generative organs (whence its name), to 

 the rectum and anus, and motor fibres to the musculature of the 

 descending colon and rectum, and have their cell-stations in the small 

 scattered ganglia of the pelvic plexus, or in terminal ganglia in the 

 walls of the viscera they supply. 



Looking at the involuntary muscles for a moment from a 

 rather different point of view, we see that they (or most of them) 

 differ from the voluntary muscles in being supplied by two sets of 

 nerve-fibres with opposite functions. In the case of the heart, we 

 have an accelerator set which course through the sympathetic, and 

 an inhibitory set which course through the vagus. In the case of 

 the blood-vessels, we have an accelerator set called vaso-constrictors, 

 and an inhibitory set called vaso -dilators. In the case of the con- 

 tractile viscera we have also viscero-accelerator and viscero-inhibitory, 

 which respectively hasten and lessen their peristaltic movements. 



