THE SYMPATHETIC NERVES 687 



of them (m : ) end about the cells of the nearest ganglion, others (w 4 , ra e ) 

 pass through several ganglia before reaching their endings, and by means of 

 collaterals may therefore act upon a number of cells. Still others find their 

 destination only when they reach ganglion cells situated far away in the 

 periphery. 



Postganglionic -fibers (g, g^ g 2 , g^ g 4 ) arise in the sympathetic ganglia 

 and, without any connection with other ganglion cells, terminate, sometimes 

 near, sometimes far away, in the free endings on smooth muscle cells, gland 

 cells, etc. Langley believes that the course of each fiber or collateral is inter- 

 rupted by one ganglion cell only. (See page 582 for Langley's use of nicotine 

 in this connection.) 



Part of the postganglionic fibers traverse the gray rami communicantes 

 to the spinal nerves and reach their destination by these paths; part of them 

 belong to branches which run an independent course to the periphery. 



The plexuses of Auerbach and Meissner, found in the wall of the alimentary 

 canal from the lowermost part of the oesophagus onward, which are commonly 

 included in the sympathetic system, present some variations from the general 

 behavior of the sympathetic nerves. For this reason they are set apart by Lang- 

 ley in a class by themselves. Nothing 1 definite can be said at present as to their 

 physiological status. 



B. COURSE OF THE SYMPATHETIC FIBERS 



According to Gaskell, the sympathetic trunk itself receives preganglionic 

 fibers only from the first thoracic to the second to fourth or fifth lumbar roots. 

 The cervical roots convey no visceral nerves; but visceral nerves are found 

 in the first or second and third sacral. These latter do not unite with the 

 sympathetic but contain fibers which are autonomic in function. 



The preganglionic fibers belonging to the sympathetic unite either with 

 cells in the ganglia of the sympathetic chain (lateral ganglia), or with cells 

 in ganglia situated farther toward the periphery (collateral ganglia). 



The following account of the course of pre- and postganglionic fibers and 

 their connections, relating to the cat, is taken from Langley. 



The cervical sympathetic receives fibers from the first to the seventh tho- 

 racic roots; in their exit from the spinal cord they are to a certain extent 

 arranged according to their function. The most powerful effect on the dilator 

 of the pupil is obtained from the first and second, on the nictitating membrane, 

 on the eyelids, etc., from the first to the third, on the submaxillary glands from 

 the second and third, on the vessels of the ear and the conjunctiva from the 

 second to the fourth, on the pilomotor nerves of the head and neck from tbe 

 fourth to the sixth. These details are mentioned because they are important 

 for a proper conception of the regeneration phenomena to be described presently. 

 All these fibers terminate in the superior cervical ganglion, the cells of 

 which send out postganglionic fibers to the plexuses about the blood vessels, to 

 certain cranial nerves, and to the three upper cervical nerves. These joining 

 the last named accompany their sensory branches to the skin and innervate the 

 erector muscles of the hair, constituting therefore the pilomotor nerves. 



The stellate ganglion receives fibers from the (third) fourth to the eighth 

 (ninth) thoracic roots. Among its postganglionic fibers pilomotor fibers pass 



