262 



THE TISSUES AND MECHANISMS OF DIGESTION. 



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

 fibres, treated of in 152. 



196. If a tube be placed in the duct, it is seen that when sapid sub- 

 stances are placed on the tongue, or the tongue is stimulated in any other 

 way, or the lingual nerve is laid bare and stimulated 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 

 produces 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 it, as at n. I.', Fig. 81, stimulation of the (front part 



v.sym. 



/u 



FIG. 81. 



^n.sym.f. n.sym.sm. vi.T^ 



-"' g.sni.a. / 



a.car. a-f- 



-~.sm.gl. 



n.sym.srri. 



r.sm.pi 



\ch.t. 



Diagrammatic Representation of the Submaxillary Gland of the Dog, with its Nerves and 

 Bloodvessels. The dissection has been on an animal lying on its back, but since all the parts 

 shown in the figure cannot be seen from any one point of view, the figure does not give the exact 

 anatomical relations of the several structures. 



sm. gld. The submaxillary gland, into the duct (sm. d.) of which a canula has been tied. The 

 sublingual gland and duct are not shown, n.l., n.l'. The lingual branch of the fifth nerve, the 

 part n.l. is going to the tongue. ch.t., ch.t'., ch.t". The chorda tympani. The part ch.t". is proceeding 

 from the facial nerve ; at ch. t'. it becomes conjoined with the lingual n.l'., and afterward diverging 

 passes as ch. t. to the gland along the duct; the continuation of the nerve in company with the 

 lingual n.l., is not shown, sm. gl. The submaxillary ganglion with its several roots, a. car. The 

 carotid artery, two small branches of which, a. sm. a. and r. sm.p., pass to the anterior and poste- 

 rior parts of the gland, v. sm. The anterior and posterior veins from the gland, falling into v.j., 

 the jugular vein. v. sym. The conjoined vagus and sympathetic trunks, g. cer. s. The upper cer- 

 vical ganglion, two branches of which, forming a plexus (a/.) over the facial artery, are dis- 

 tributed (w. sym. sm.) along the two glandular arteries to the anterior and posterior portions of the 

 gland. 



The arrows indicate the direction taken by the nervous impulses during reflex stimulation of 

 the gland. They ascend to the brain by the lingual and descend by the chorda tympani. 



of) tongue produces, under ordinary circumstances, no flow. This shows 

 that the centre of the reflex action is higher up than the point of section ; it 

 lies in fact in the brain. 



In the angle between the lingual and the chorda, where the latter leaves the 

 former to pass to the gland, lies the small submaxillary ganglion (represented dia- 

 grammatically in Fig. 81, sm. gl). This consists of small masses of nerve-cells 



