DIGESTION 363 



sublingual ganglion, since its cells, as well as the others in the 

 chordo - lingual triangle, are the cells of origin of axons 

 which proceed as non-medullated fibres to the sublingual gland. 

 The sublingual gland receives its cerebral fibres partly from 

 branches given off from the lingual in the chordo-lingual triangle 

 after the chorda tympani proper has separated from it, and ending 

 around the nerve-cells within that triangle, partly from the chorda 

 itself in the terminal portion of its course. These statements rest on 

 anatomical and physiological evidence. The latter we shall return to. 



The cerebral fibres for the parotid (in the dog) pass from the 

 tympanic branch of the glosso-pharyngeal (Jacobson's nerve) through 

 connecting filaments to the small superficial petrosal branch of the 

 facial, with this nerve to the otic ganglion, and thence by the 

 auriculo-temporal branch of the fifth to the gland. 



The sympathetic fibres for all the salivary glands appear to arise 

 from nerve-cells in the upper dorsal portion of the spinal cord. 

 Issuing from the cord in the anterior roots of the upper thoracic 

 nerves (first to fifth, but mainly second thoracic for the submaxillary), 

 they enter the sympathetic chain, in which they run up to the 

 superior cervical ganglion. Here they break up into terminal 

 twigs, and thus come into relation with ganglion cells, whose 

 axons pass out as non-medullated fibres, and, surrounding the 

 external carotid, reach the salivary glands along its branches. 

 Langley has shown, by means of nicotine (p. 165), that the sym- 

 pathetic fibres for the submaxillary and sublingual, and, indeed, for 

 the head in general in the dog and cat, are connected with nerve- 

 cells in this ganglion, but not between it and their termination, or 

 between it and their origin from the spinal cord. 



Stimulation of the Cranial Fibres. When in a dog a cannula 

 is placed, in Wharton's duct, and the saliva collected (p. 424), 

 it is found that stimulation of the peripheral end of the divided 

 chorda causes a brisk flow of watery saliva, and at the same 

 time a dilatation of the vessels of the gland, which we have 

 already described in dealing with vaso-motor nerves (p. 163). 

 Notwithstanding the vaso-dilatation, the volume of the gland is 

 in general diminished, owing to the rapid passage of water into 

 the duct (Bunch). The blood has been shown to lose water in 

 making the circuit of the submaxillary gland during excitation of 

 the chorda, but doubtless some of the water of the saliva comes 

 directly from the cells or from the lymph. That the increased 

 secretion is not due merely to the greater blood-supply, and the 

 consequent increase of capillary pressure, is shown by the 

 injection of atropine, after which stimulation of the nerve, 

 although it still causes dilatation of the vessels, is not followed by 

 a flow of saliva. Mere increase of pressure could not in any case 

 of itself account for the secretion, since it has been found that 

 the maximum pressure in the salivary duct when the outflow of 

 saliva from the duct is prevented may, during stimulation of the 

 chorda, much exceed the arterial blood-pressure (Ludwig). In 

 one experiment, for example, the pressure in the carotid of a dog 

 was 125 mm., in Wharton's duct 195 mm. of mercury. 



