VASOMOTOR REFLEXES 235 



gland. They come from the facial and pass by way of the chorda tympani to 

 the lingual. In the same path are found also the dilator nerves for the anterior 

 two-thirds or three-fourths of the tongue. The dilator fibers for the posterior 

 part of the tongue, for the anterior pillars of the fauces, and the tonsils run in 

 the trunk of the glossopharyngeal. 



The vasodilator fibers of the mucous membrane of the lips, the cheeks, the 

 hard palate and the external nares, as well as of the corresponding parts of 

 the skin of the face comes from the second to the fifth thoracic nerves, traverse 

 the cervical sympathetic and unite for the most part with the trigeminal, which 

 itself also contains fibers of this kind for the face and for the eye (Dastre and 

 Morat). 



The ear gets its dilator fibers from the eighth cervical and first thoracic 

 nerves. 



The dilator nerves of the anterior extremities leave the spinal cord from the 

 fifth to the eighth thoracic : those of the posterior extremities probably in the 

 second to the fourth lumbar nerves. Here we meet with the remarkable circum- 

 stance that the latter nerves pass out exclusively in the posterior roots of the 

 lumbar nerves (Strieker, Bayliss; cf. Chapter XXII). The presence of vaso- 

 dilator nerves in the posterior roots of the brachial plexus has been asserted 

 also. We have the following facts with regard to the dilator nerves of the 

 abdominal organs: Vasodilator fibers in abundance are found in the second to 

 twelfth thoracic as well as in the first and second lumbar nerves of the dog : the 

 twelfth and thirteenth thoracic contain a number of these in their dorsal roots; 

 the splanchnics and the upper thoracic nerves contain the vasodilator fibers 

 for the organs of the abdomen. 



The vagus is said, to convey vasodilator nerves for the coronary arteries of 

 the heart. Most of the dilator nerves for the coronary vessels however traverse 

 the sympathetic pathways. They probably pass out of the spinal cord, and 

 reach the heart by way of the stellate ganglion (cf. Fig. 67, page 191). 



According to some authors the lungs receive dilator fibers from the cervical 

 sympathetic as well as from the vagus. 



The vessels of the mucous membrane of the larynx are provided with dilator 

 nerves from the superior laryngeal. 



Vasodilator nerves which play an essential role in the erection of the penis 

 pass to that organ by way of the anterior roots of the first to the third sacral 

 nerves, and the hypogastric plexus. 



11. VASOMOTOR REFLEXES 



Like the cardiac nerves, the vasomotor nerves are stimulated reflexly, and 

 the blood supply to the various organs as well as the arterial blood pressure 

 is variously influenced. 



We have different observations tending to show that vasomotor reflexes can 

 be discharged by the vessels themselves, so that the vessels may be said to 

 participate in the reflex regulation of their own functions. We know also 

 that these reflexes are set up by all other possible kinds of afferent nerves. 



The reflex takes effect primarily in the same vascular region whence came 

 the afferent impulse. Possibly the congestion which has long been known to 

 take place on rubbing or warming the skin belongs to this class of reflexes, 

 also the congestion which is seen in the intestine when the abdominal cavity 

 is opened. 



