HEAD AND NECK IN SECTION 



13 



we have the pendulous pahue. From the position of the pendulous 

 palate and its relation to the epiglottis, it will be seen that, excepting 

 during the act of deglutition, the buccal cavity is effectively shut off from 

 that of the pharynx, thus rendering the process of respiring through the 

 mouth a most difficult one in the horse. 



Passing backwards from the inferior part of the nasal chamber we 

 have the right division of the posterior nares. It places the inferior 

 meatus into direct communication with the pharynx, and excepting 

 during deglutition, it is quite patent. A reference to the plate will 

 show that a curved line with the concavity downwards would indicate 

 the continuity of this meatus with the rima glottidis through the 

 pharynx. 



While the act of deglutition is being carried out, however, there is a 

 marked alteration in the relationship of the structures of this region to 

 one another. The dorsum of the tongue is arched by the stylo-glossi 

 muscles, and the soft palate is raised and stretched by the levator and 

 tensor palati muscles. Thus the opening of the posterior nares is shut ^^ -^ 

 off and the dorsum of the tongue is rendered an inclined plane down c^ qJ 

 which the bolus of food passes until it is grasped by the constrictor ,0 q 

 muscles of the pharynx. The genio-hyoid, the anterior belly of the *^ o 

 digastricus, and the mylo-hyoid muscles cause the whole larynx to rise, ';_. . 

 the epiglottis is drawn downwards and the rima glottidis is closed, so {- 

 that the plane formed by the dorsum of the tongue is now in a straight ;.^ 

 line with the oesophageal opening from the pharynx, the line having f 

 a slight inclination downwards and backwards. ^' 



It is of most urgent importance to note the relationship to one 

 another of the various structures of this region, and from what has 

 been said the advisability of allowing the animal to voluntarily perform 

 the act of deglutition during the passage of the probang, or the 

 administration of a bolus, etc. is apparent. 



In the same plate the right outer wall of the membranous vestibule, 

 the pharynx, is shown. This chamber is regularly cylindrical in form. 



