32 8 TEXT-BOOK OF PHYSIOLOGY. 



the vaso-motor nerves, which come from the central nervous system, 

 terminate, breaking up into tufts, which arborize around the nerve- 

 cells. From the cells new nerve-fibers arise which then pass without 

 interruption to their final destination. 



-=<The nerve-fibers which emerge from the central nerve system 

 are extremely fine in caliber and medullated; those which emerge 

 from the sympathetic ganglia are equally fine, but non-medullatedc^ 

 The former are termed pre-ganglionic, the latter post-ganglionic 

 fibers. The ganglion in which the pre-ganglionic fibers end is not 

 necessarily found in the pre-vertebral or lateral chain; it may be 

 found in the collateral or even in the peripheral group. 



VThe vaso-constrictor nerves take their origin from nerve-cells 

 located in the anterior horns and lateral gray matter of the spinal 

 cord.^They emerge from the cord in company with the fibers which 

 compose the anterior roots of the spinal nerves from the second 

 thoracic to the second or third lumbar nerves inclusive.^ A short 

 distance from the cord they leave the anterior roots as the white rami 

 communicantes and enter the pre-vertebral or lateral sympathetic 

 ganglia^ From the results of many observations and experiments 

 it is prooable that the great majority of the vaso-constrictor nerves 

 terminate in these ganglia; that is to say, it is here that the pre- 

 ganglionic fibers arborize around the contained nerve-cells. From 

 the nerve-cells new fibers arise, the post-ganglionic, which pass to the 

 blood-vessels of the head, to the upper and lower extremities, and to 

 the thoracic and abdominal viscera. The vaso- constrictors for the 

 head emerge from the spinal cord in the first four thoracic nerves, 

 thence successively into and through the ganglion stellatum (the first 

 thoracic), the annulus of Vieussens, the inferior cervical ganglion, 

 the sympathetic cord to the superior cervical ganglion, around the 

 cells of which they arborize. From this ganglion the new fibers 

 follow the carotid artery and its branches to their terminations. 



The vaso-constrictors for the fore-limbs emerge from the cord in 

 the roots of the fourth to the tenth thoracic nerves inclusive. Through 

 the white rami they pass into the sympathetic chain, after which they 

 take an upward direction and terminate around the cells of the gan- 

 glion stellatum. From this ganglion the new fibers enter, by way of 

 the gray rami communicantes, the trunks of the cervical nerves which 

 unite to form the brachial plexus and by this route pass to the blood- 

 vessels. 



The vaso-constrictors for the hind-limbs emerge from the cord 

 in the roots of the eleventh dorsal to the second or third lumbar nerves 

 inclusive. They then pass through the white rami to the lower 

 lumbar and upper sacral ganglia. Thence by way of the gray 

 rami they pass into the nerve-trunks which unite to form the sacral 

 nerves and by this route pass to the blood-vessels. 



