384 TEXT-BOOK OF PHYSIOLOGY 



the cells of this ganglion post-ganglionic fibers pass to the walls of the 

 blood-vessels of the parotid gland and of the cheek and gums. 



The sacral vaso-dilatator nerve fibers consist of two consecutively 

 arranged neurons, a pre- and a post-ganglionic. The pre-ganglionic fibers 

 have their origin in nerve-cells in the gray matter of the lumbar or sacral 

 region of the spinal cord. From these cells they pass into the ventral 

 roots of the second and third sacral nerves to be ultimately distributed by 

 way of the pelvic nerve to sympathetic ganglia in the pelvic region around 

 the cells of which their terminal branches arborize. From these ganglia 

 post-ganglionic fibers emerge which pass to the blood-vessels of the organs of 

 generation and adjacent structures. 



2. The spinal vaso-dilatator nerves, i.e., those dilatator fibers found 

 in the trunks of the spinal nerves and distributed to the blood-vessels of 

 the skin of the fore and hind limbs and the body walls, differ from the 

 foregoing in their anatomic arrangement, origin and function. For 

 reasons to be stated below they have been termed 



Antidromic Vaso-dilatator Nerves. Though it has been generally 

 believed that these vaso-dilatator fibers have their origin in nerve-cells 

 in the ventral horns of the gray matter, that they pass outward through 

 the ventral roots of the thoracic and lumbar nerves, that they belong to 

 the efferent system of nerves, yet these facts have never been positively 

 determined. While this may be the correct interpretation doubt has 

 been thrown upon it by the investigations of Bayliss. From the results 

 of a long series of experiments this investigator concludes that vaso- 

 dilatator nerves for the regions of the body just mentioned, do not leave 

 the spinal cord in the ventral roots; that the vaso-dilatation observed 

 on stimulation of the mixed spinal nerve is due to the presence of nerve- 

 fibers that do not differ from the ordinary afferent or sensor, posterior 

 or dorsal root fibers; that these nerve-fibers, moreover, have their origin in the 

 nerve-cells of the ganglia of the dorsal roots. From the fact that they trans- 

 mit nerve impulses to blood-vessels in a direction contrary to that of other 

 afferent nerve-fibers, the term antidromic has been given to them. The 

 centers from which they arise are capable apparently of being aroused to 

 activity by impulses transmitted to them from other regions of the body. 



These statements are based on the following facts: Stimulation of the 

 peripheral ends of the divided dorsal roots of the upper thoracic and lumbo- 

 sacral nerves gives rise to vascular dilatation in the upper and lower limbs; 

 separation from the cord is not followed by their degeneration, hence they 

 are not efferent nerves; extirpation of the ganglia of the dorsal roots is, 

 however, followed by their degeneration, hence their trophic centers are 

 in these ganglia. Whether the blood-vessels of the abdominal viscera which 

 apparently receive vaso-dilatator nerve impulses are supplied by nerves 

 having the foregoing origin and action, is a subject for further investigation. 



The course, distribution, and functions of the vaso-dilatator nerves have 

 bee,n determined by the same methods as those employed in the investigation 

 of the vaso-constrictor nerves. Thus division and stimulation of the pe- 

 ripheral branches of the nerve of Wrisberg, e.g., the great petrosal and the 

 chorda tympani, is followed by an active dilatation of the blood-vessels of 

 the nasal chambers and palate, and of the blood-vessels surrounding the sub- 

 maxillary and sublingual gland. The inflow of blood is so great that the 



