i5o TEXT-BOOK OF PHYSIOLOGY. 



tents. The blood-vessels possess that degree of dilatation necessary for 

 nutritive purposes. 



With the introduction of food into the mouth and the onset of mastication 

 the blood-vessels suddenly dilate, the blood-supply is increased, and the 

 gland-cells begin to discharge water, inorganic salts, and their organic 

 constituents into the lumen of the acinus, materials that collectively consti- 

 tute the saliva characteristic of any one of the glands. This continues until 

 mastication ceases, when all the structures return to their former condition 

 of relative inactivity. 



The nerves and nerve centers that constitute the nerve mechanism for 

 the secretion of saliva, as determined by experimental investigations are 

 shown in the following table: 



Afferent Nerves. Nerve-centers. Efferent Nerves. 



1. Lingual and buccal branches of Medulla oblongata. The chorda tympani and its post- 



the trigeminal nerve. ganglionic continuations for the sub- 



maxillary and sublingual glands; 

 the glosso-pharyngeal nerve and its 

 postganglionic continuations con- 

 tained in the auriculo-temporal 



2. Taste fibers in the chorda branch of the trigeminal nerve, for 



tympani. the parotid gland. 



3. Taste fibers in the glosso- The sympathetic nerve for all the 



pharyngeal. glands. 



The Efferent Nerves. The efferent nerve-fibers, as stated in the fore- 

 going paragraph, that transmit nerve impulses to the submaxillary, sub- 

 lingual, and parotid glands, as well as to their associated blood-vessels, are 

 contained respectively in the chorda tympani and its postganglionic con- 

 tinuations, in the glosso-pharyngeal and its postganglionic continuations 

 contained in the auriculo-temporal branch of the fifth nerve, and in the 

 branches of the sympathetic nerve derived from the superior cervical ganglion. 

 That these nerves transmit the nerve impulses to the salivary apparatus is 

 shown by the effects that follow their division and stimulation. 



The Chorda Tympani. The chorda tympani nerve is apparently a 

 branch of the facial, the trunk of which it leaves in the aqueduct of Fallopius. 

 It then crosses the tympanic cavity, emerges through the Glaserian fissure, 

 and joins the lingual branch of the inferior maxillary division of the fifth 

 nerve. After passing forward as far as the sublingual gland, nearly all of 

 the fibers leave the lingual nerve by four or five strands to become connected 

 by terminal branches with nerve ganglion cells in relation with the sub- 

 maxillary and sublingual glands. (See Fig. 67.) 



The effects on the secretion and flow of saliva from the submaxillary 

 gland which follow division and stimulation of the chorda tympani nerve 

 are shown in the following way: A cannula is inserted into Wharton's duct 

 and the rate of flow estimated; the nerve is then divided, after which the 

 flow ceases. The peripheral end of the nerve is then stimulated with 

 induced electric currents when a copious secretion of a thin saliva takes 

 place, accompanied by a marked dilatation of the blood-vessels of the gland. 

 The quantity of blood passing through the vessels is so great as to give to 

 the venous blood an arterial hue and to the small veins a distinct pulsation. 

 It would appear from these effects that the chorda contains two sets of fibers, 



