THE VASOMOTOR NERVES. 545 



These latter waves are also due to a rhythmical action of the 

 vasomoter center. During sleep certain much longer, wave-like 

 variations in the blood-pressure also occur that are again due 

 doubtless to a rhythmical change of tone in the vasoconstrictor 

 center. 



General Course and Distribution of the Vasodilator Fibers. 

 By definition a vasodilator fiber is an efferent fiber which when 

 stimulated causes a dilatation of the arteries in the region supplied. 

 In searching for the existence of such fibers in the various nerve 

 trunks physiologists have used all the methods referred to above, 

 namely, the flushing of the organ as seen by the eye, the increased 

 blood-flow, the increase in volume, or the fall in blood-pressure on 

 the arterial side associated with a rise on the venous side. By 

 these methods vasodilator fibers have been demonstrated in the 

 following regions : 



1. In the facial nerve. The dilator fibers are found in the chorda tym- 



pani branch and are distributed to the salivary glands (submaxil- 

 lary and sublingual) and to the anterior two-thirds of the tongue. 



2. In the glossopharyngeal nerve. Supplies dilator fibers to the posterior 



third of tongue, tonsils, pharynx, parotid gland (nerve of Jacobson). 



3. In the sympathetic chain. In the cervical portion of the sympathetic 



dilator fibers are carried which are distributed to the mucous mem- 

 brane of the mouth (lips, gums, and palate), nostrils, and the skin 

 of the cheeks. These fibers pass up the neck to the superior cervi- 

 cal ganglion and thence by communicating branches reach the Gas- 

 serian ganglion and are distributed to the bucco-facial region in the 

 branches of the fifth cranial nerve.* From the thoracic portion of 

 the sympathetic vasodilator fibers pass to the abdominal viscera by 

 way of the splanchnic nerves and to the limbs by way of the 

 branches of the brachial and lumbar plexuses, but the data regarding 

 the dilator fibers for these regions are not as yet entirely satisfactory. 

 Goltz and others have shown that dilator fibers are found in the 

 nerves of the limbs, but the origin of these fibers from the sympa- 

 thetic chain has not been demonstrated. 



4. In the nervi erigentes. Eckhard first gave conclusive proof that the 



erection of the penis is essentially a vasodilator phenomenon. The 

 fibers arise from the first, second, and third sacral spinal nerves, pass 

 to the hypogastric plexus as the nervi erigentes, and thence are dis- 

 tributed to the erectile tissues of the penis. 



The General Properties of the Vasodilator Nerve Fibers. 

 Unlike the vasoconstrictors, the vasodilators are not in tonic 

 activity; at least, no experimental proof has been given that they 

 are. In the case of the erectile tissue of the penis and the dilators 

 of the glands it would seem that the fibers are in activity only 

 during the functional use of the organ, at which time they are 

 excited reflexly. There has been much discussion in physiology as 

 to the nature of the action of the dilator fibers. The muscular 

 coat of the small arteries runs transversely to the length of the 



* See " Recherches experimentales sur le systeme nerveux vasomoteur, " 

 Dastre and Morat, 1884. 

 35 



