DIGESTION IN THE MOUTH. 



275 



opening into the parotid duct before it reaches the mouth, 

 readily performed iirthe horse or dog (Fig. 111). 



This may be 



To make a parotid fistula in the dog, the animal usually employed in these 

 experiments, the hair is first shaved from the cheek, between the eye and the angle 

 of the mouth. On running the finger along the lower border of the zygomatic 

 arch, just before it is inserted into the superior maxilla, a slight notch is felt. It 

 is just at this point that the duct passes into the mouth. After chloroforming the 

 animal, an incision is made through the skin from this point, cutting obliquely in 

 a direction from the inner canthus of the eye to the angle of the mouth, passing 

 through the subcutaneous cellular tissue, when the facial artery and vein, branches 

 of the facial nerve, and parotid duct are found together, the duet pearly white in 

 hue, passing horizontally across the fibres of the masseter muscle parallel to the 

 nerve, usually about a quarter of an inch below it, while the artery and vein run 

 from above downward (Fig. 112). The vessels and nerves must be carefully 

 removed from before the duct, which is to lie isolated and closed as near the 

 mouth as possible with a clip. A cannula may then be inserted into the duct. If 

 it is decided to retain the fistula permanently, the duct must be freed from the 

 connective tissue for as long a distance as possible, divided, and then brought out 

 at the angle of the wound, which is to be closed with sutures, one passing through 

 the duct to retain it in position. After a few days, when the wound is healing, 

 the duct will mortify and drop out, leaving a fistulous track to the gland, which 

 must be kept open by the daily passage of a fine probe, as it has a decided ten- 

 dency to close. A similar operation is readily performed upon the horse or ox, 

 where the large size of the duct renders it easily recognizable. After a cannula 

 has been inserted into the duct of the animal, its free extremity may be connected 

 by a piece of rubber tubing with a rubber bulb or glass bottle, in which the saliva 

 may be collected (Figs. 113 and 114). 



Fig. 113.— Parotid Duct in the Horse. (Bernard.) 

 The dotted line indicates the contour of the gland and the course of the duct of Steno. 



The parotid gland of the horse is only in activity when the animal 

 is masticating food, while the parotid glands of the ruminants are con- 

 tinually secreting. The parotid glands constitute almost entirely the 

 posterior or serous system of the salivary glands, and furnish by far the 

 largest amount of the fluid which impregnates the food. The parotid 



