THE CRANIAL NERVES. 477 



it sends to the submaxillary gland. A similar influence is exerted on 

 the circulation in the corresponding half of the tongue ; and it is of 

 special importance that this increase of circulatory activity, excited by 

 galvanizing the chorda tympani above its union with the lingual, is 

 also produced, according to Yulpian,* by galvanizing the separated 

 extremity of the divided lingual nerve containing fibres of the chorda 

 tympani. This shows that its influence is in the nature of a motor 

 action ; that is. it passes from the central parts toward the periphery, 

 and not in the inverse direction. Finally, while evulsion of the facial 

 nerve from the aqueduct of Fallopius arrests the secretive action of the 

 submaxillary gland, its section at the stylomastoid foramen does not 

 have this effect, but only paralyzes the muscles of the face. This dif- 

 ference depends on the fact that in the former case the chorda tym- 

 pani is involved in the injury, in the latter it remains intact. 



Another symptom observed in deep-seated lesions of the facial nerve, 

 and also dependent on injury of the chorda tympani, is a disturbance 

 of the sense of taste in the tip and surface of the tongue. In this 

 affection, the taste is not absolutely abolished, but is diminished in 

 acuteness and in promptitude. If a bitter substance be placed alter- 

 nately on the two sides of the tongue, it is perceived almost imme- 

 diately on The sound side, but only after a considerable interval on the 

 side of the paralysis. Various explanations have been suggested for 

 these phenomena, which by most writers are referred exclusively to 

 the chorda tympani. As the fibres of this nerve have so marked an 

 influence on the circulation in the tongue and on salivary secretion, 

 it is plain that when these functions are depressed by its division or 

 injury the sense of taste may be impaired as an indirect result. But 

 whatever be the mechanism of its action, there is no question that its 

 paralysis interferes, to an appreciable degree, with this sense ; and an 

 alteration of taste, accompanying facial paralysis on the same side, 

 consequently fixes the location of the nervous lesion at some point 

 within the stylomastoid foramen. 



Eighth Pair. The Auditory, 



On the posterior surface of the medulla oblongata, a little behind the 

 widest part of the fourth ventricle, a number of white striations run 

 from the neighborhood of the median line transversely outward, toward 

 the peduncles of the cerebellum. These striations represent the roots 

 of the auditory nerve. The nucleus from which they originate is a 

 mass of gray substance beneath them, containing nerve cells of the 

 smaller variety. It extends outward and upward toward the white 

 substance of the cerebellum, with which it is connected by numerous 

 radiating fibres. 



From this nucleus the root fibres run almost horizontally outward, 

 and, uniting with each other, curve round the inferior peduncle of the 



* Comptes Kendus de 1' Academic des Sciences. Paris, 1879, tome Ixxxiz., p. 274. 



