348 VETERINAEY PHYSIOLOGY 



are put in a dog's mouth a profuse secretion of very watery 

 saliva ensues to wash them out. When flesh is given a saliva 

 rich in mucin is produced. When dry food is given saliva 

 is produced in greater quantity than when moist food is 

 supplied. Pavlov further states that the sight of different 

 kinds of food produces a flow of the kind of saliva which their 

 presence in the mouth would produce. 



II. SWALLOWING 



The food after being masticated is collected on the surface 

 of the tongue by the voluntary action of the buccinators and 

 other muscles, and then, the point of the tongue being pressed 

 against the hard palate behind the teeth, by a contraction 

 of the tongue passing from before backwards, the bolus of 

 food is driven backwards. When the posterior part of the 

 tongue is reached the act becomes purely reflex, and the food 

 is forced through the pillars of the fauces into the pharynx. 

 It is prevented from passing up into the posterior nares by 

 the contraction of the palato-pharyngeus muscle, and of the 

 levatores palati. 



The larynx is pulled upwards as a whole by the stylo-hyoid 

 and stylo-thyroid and the thyro-hyoid muscles, and the entrance 

 of food is prevented by the closure of upper part of aperture. 

 The arytenoid cartilages are pulled forward by the thyro- 

 arytenoid muscles, and approximated by the arytenoidei, while 

 a cushion on the posterior surface of the epiglottis becomes 

 .applied to their tips, forming a tri-radiate fissure or chink 

 through which food cannot pass. The lateral crico-arytenoids 

 also approximate the vocal cords, and close the glottis. 



The constrictors of the pharynx contract from above down- 

 wards, and force the food into the grasp of the oesophagus, and 

 this by a slow peristaltic contraction sends the food onwards to 

 the stomach. This peristalsis is abolished by section of the 

 vagi, and it is generally not essential to swallowing. In 

 swallowing liquids it is not brought into play, but the fluid 

 is forced by the tongue down the relaxed oesophagus into 

 the stomach. 



The passage of the food into the stomach may be heard as a 



