CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 333 



187. The submaxillary gland is supplied with two sets of 

 nerves. These are represented in Fig. 76, which is a very dia- 

 grammatic rendering of the appearances presented when the sub- 

 maxillary gland is prepared for an experiment in a dog, the 

 animal being placed on its back and the gland exposed from the 

 neck. The one set, and that the more important, belongs to 

 the chorda tympani nerve (ch.t ff ). This is a small nerve, which 

 branches off from the facial or seventh cranial nerve in the Fallo- 

 pian canal before the nerve issues from the skull. Whether it 

 really belongs to the facial proper has been doubted ; in man the 

 fibres which form it are either fibres coming not from the roots of 

 the facial proper, but from the portio intermedia Wrisbergi, or, 

 according to some, fibres which though joining the facial in the 

 Fallopian canal are ultimately derived from another (the fifth) 

 cranial nerve. Leaving the facial nerve the chorda tympani 

 passes through the tympanic cavity or drum of the ear (hence 

 the name) and joins or rather runs in company (ch.t f ) with the 

 lingual or gustatory branch of the fifth nerve. Some of the fibres 

 run on with the lingual right down to the tongue (these are not 

 shewn in the figure), but many leave the lingual as a slender nerve 

 (ch.t), which reaching Wharton's duct or duct of the submaxillary 

 gland (sm.d) runs along the duct to the gland. As the nerve 

 courses along the duct nerve cells make their appearance among 

 the fibres, and these are especially abundant just after the duct 

 enters the hilus of the gland. The fibres may be traced into the 

 gland for some distance, but as we have said their ultimate end- 

 ing has not yet been definitely made out. Along its whole course 

 up to the gland, the fibres of the chorda are very fine medullated 

 fibres, but they lose their medulla in the gland. 



The other set of nerve-fibres reaches the gland along the small 

 arteries of the gland. These are non-medullated fibres mixed 

 with a few medullated fibres and may be traced back to the 

 superior cervical ganglion. From thence they may be traced 

 still further back down the cervical sympathetic to the spinal 

 cord, following apparently the same tract as the vaso-constrictor 

 fibres, treated of in 144. 



188. If a tube be placed in the duct, it is seen that when 

 sapid substances are placed on the tongue, or the tongue is stimu- 

 lated in any other way, or the lingual nerve is laid bare and stimu- 

 lated with an interrupted current, a copious flow of saliva takes 

 place. If the sympathetic be divided, stimulation of the tongue 

 or lingual nerve still produces a flow. But if the small chorda 

 nerve be divided, stimulation of the tongue or lingual nerve pro- 

 duces no flow. 



Evidently the flow of saliva is a nervous reflex action, the 

 lingual nerve serving as the channel for the afferent and the 

 small chorda nerve for the efferent impulses. If the trunk of 

 the lingual be divided above the point where the chorda leaves 



