470 PHYSIOLOGY 



to the seventh thoracic anterior roots, and have their cell stations in the 

 superior cervical ganglion. They travel as small medullated nerve fibres 

 from the white rami up the sympathetic chain, through the stellate ganglion 

 and ansa Vieussenii and up the cervical sympathetic. 



(2) The next set of nerve fibres have their cell station in the stellate 

 ganglion. The white rami arise from the fifth to the eighth thoracic nerves, 

 while the grey rami pass to the nerve roots from the third cervical nerve 

 to the fourth thoracic nerve. 



(3) The remaining nerves, supplying all the rest of the body and tail, arise 

 by the white rami from the seventh thoracic to the third or fourth lumbar 

 nerve, and are distributed as grey rami to all the spinal nerves below 

 the fourth thoracic. 



We thus see that, in speaking of the functions of a spinal nerve root, we 

 must clearly distinguish whether we mean the root as it arises from the 

 spinal cord, in which case its visceral functions will include those of its white 

 ramus, or whether we mean the made-up or complete spinal nerve after it has 

 received its grey ramus (Fig. 239). In the latter case the visceral functions 

 of the root will be more restricted than in the former case, and will have a 

 different distribution. In stimulating the nerve roots in the spinal canal 

 it is sometimes possible, by weak stimuli, to display the functions of the 

 corresponding white ramus, and then by increasing the stimulus to get 

 superadded the effects due to the excitation of the grey ramus in the made-up 

 nerve, in consequence of the spread of current. 



" When, for example, the eleventh thoracic anterior roots are stimulated in the 

 spinal canal with weak shocks, a fairly long strip of hairs in the lumbar region will 

 be erected, the maximum movement of the hairs being near the middle of the strip. 

 This marks the area of distribution of the pilomotor nerves given by the eleventh thoracic 

 nerve to the sympathetic. If then the strength of the shock be increased to a certain 

 point, the hairs in the long strip will of course be erected as before, but in addition 

 thero will be energetic erection of hairs in a short strip a little distance above the long 

 strip, and separated from it by a quiescent region. This short strip is the same as that 

 affected by stimulating the grey ramus or the dorsal cutaneous branch of the eleventh 

 thoracic nerve. It marks the area of distribution of the pilomotor fibres received 

 l>\ the spinal nerve from the sympathetic." (LANGLEY.) 



We may now indicate briefly the main course and functions of the fibres 

 of the sympathetic system. 



(1) The head and neck are supplied by fibres leaving the spinal cord 

 by the first five dorsal nerves (chiefly by the second and third). They .ill 

 have their cell station in the superior cervical ganglion. They convey : 



Vaso-constrictor impulses to the blood vessels. 

 Dilator fibres to the pupil. 



Secretory fibres to the salivary glands and sweat glands. 

 Vaso-dilator fibres to the lower lip and pharynx (?). 



(2) The thoracic viscera (heart and lungs) are supplied by the same five 

 nerve roots. The cell station of these fibres is however situated in the 

 stellate ganglion. They convey : 



Accelerator or augmentor impulses to the heart. 



