LESSON XLIV 



DIGESTION (Continued) 



SECRETION OF SALIVA 



1. Isolation of the Secretory Nerves. Anesthetize a mammal and 

 maintain the anesthesia throughout the following experiments until the 

 animal has been killed. Perform tracheotomy. Expose the left com- 

 mon carotid artery and insert in its central end a straight cannula. On 

 the opposite side make a longitudinal cut through the skin a little to 

 one side of the median line, and beginning at a point opposite the canine 

 teeth. Prolong it backward to the angle of the jaw. Cut through the 

 platysma myoides. The next layer of muscle-fibers is arranged trans- 

 versely. Carefully split this layer (muse, mylohyoideus) with forceps, 

 reflecting its halves to the right and left. Let the assistant place his 

 index-finger upon the floor of the mouth and pull it away from the side 

 of the lower jaw. Identify the lingual nerve which passes transversely 



FIG. 120. SCHEMA ILLUSTRATING THE NERVE SUPPLY OF THE SUBMAXILLARY GLAND. 

 SG, Submaxillary gland; supplied by a small artery from the carotid system (CA). 

 It is drained by a small vein which generally enters the facial (FV) at its point of con- 

 fluence with the lingual vein (LV). The external (ESV) and internal (JSV) maxillary 

 veins invest the gland and unite to form the external jugular vein (EJV). The sympa- 

 thetic nerve supply is derived from the sup. cerv. ganglion (SCG). The chorda tympani 

 (CT) attaches itself to the lingual nerve LN and then to Wharton's duct (W) ; S, lower 

 jaw. 



across the floor of the mouth at about the junction of the middle and 

 posterior thirds of the jaw. Follow the latter in a central direction until 

 you reach J:he chorda tympani nerve and the duct of the submaxillary 

 gland (Wharton's). Isolate the chorda tympani nerve at the point 

 where it leaves the lingual nerve, and place it in shielded electrodes. 

 Ligate the duct of the submaxillary gland and stimulate the chorda 

 tympani for a few seconds, so as to distend the duct with saliva. Insert 

 a cannula. Expose the vagosympathetic nerve of the same side, cut 

 it, and arrange for stimulating its central end (toward the head) with a 

 weak tetanizing current. 



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