308 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



and the bolus of food forced from the mouth into the pharynx. Almost 

 at the same time the hyo-glossal muscles also begin contracting and, 

 especially those portions which are attached to the cornua of the hyoid, 

 cause the free surface of the tongue, which at rest looks upward and 

 backward, to move backward and downward upon the epiglottis and 

 mechanically close the glottis. The rapid narrowing of the space between 

 the mylo-hyoids and the palate which is thus brought about also rapidly 

 raises the pressure there. This effect is increased by the pull of the 

 hyo-glossal muscles, which gives the tongue a backward and downward 



Fig. 129.— Median Section of the Human Head, after Hknle. 



(J/CTJ/CI-.) 



Vp, the position of the soft palate during rest ; 1. ovificB of Eustachian tirte ; Vol and Vc2 nrst a.. ■ 



art il age; 3, thyroid 



movement. Tims, liquids and soft foods are squirted down the entire 

 pathway to the stomach before contractions of the pharyngeal or 

 oesophageal muscles can manifest themselves (Meltzer). Fragments 

 which happen to remain in the pharynx are sent down later by the suc- 

 ceeding contraction of the constrictors and with a slowness peculiar to 

 these muscles (Fig. 130). When the bolus lias passed the anterior pala- 

 tine arches its return to the mouth is prevented by contraction of the 

 palato-glossi muscles which lie in the anterior pillar of the fauces, and, 



