310 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



the opening of the oesophagus and hinder its passage into the nasal 

 chambers and windpipe. As soon as the bolus of food reaches the 

 anterior palatine arches the soft palate is raised by the contraction of 

 the levator-palati muscles, and rendered tense and directed backward 

 toward the posterior walls of the pharynx, with which, in many animals, 

 as in the horse, it comes in actual contact (Fig. 131), and at the same 

 time the palatopharyngeal muscles, which lie in the posterior arches of 

 the fauces, contract. These muscles have a bony insertion in the posterior 

 wall of the pharynx, and then are inserted into the soft palate. The 

 action of the levator-palati muscles has the effect of giving these muscles 

 fixed points of support. In their condition of rest they form a curved 

 line on each side from the centre to the back of the pharynx. When 



Fig. 131.— Anteroposterior Section of the Head of the Horse, show- 

 ing the Entire Mouth, Pharynx, and Nasal Cavities. (Gamgec.) 

 1, genio-hyoglossus ; 2, genio-hyoideus ; 3, section of the soft palate; 4, pharynx; 5, (Esophagus ; 6, 

 guttural pouch ; 7, pharyngeal opening of the Eustachian tube ; 8, cavity of the larynx ; 9, ventricle of 

 the larynx ; 10, trachea ; 11, superior turbinated bone ; 12, inferior turbinated bone ; 13, ethmoid cells ; 

 14, portion of the cranial cavity which lodges the brain proper ; 15, portion of the same which lodges the 

 cerebellum ; 16, falx cerebri ; 17, tentorium ; 18, upper lip ; 19, lower lip. 



these muscles contract, downward motion of the soft palate having been 

 prevented by the action of the levator-palati muscles and approxima- 

 tion of their origin and insertion being thus prevented, the effect will 

 be to form a straight line between these two points. Merkel states that 

 the inferior portions of the phaiyngo-palatine muscles cross in the 

 middle line" of the posterior wall of the pharynx, and thus act as a 

 sphincter in shutting off the nasal portion of the pharynx, the two 

 muscles forming a circular muscle, like the orbicularis oris. The dis- 

 tribution of these fibres is shown in Fig. 132. As a consequence, the 

 posterior pillars of the fauces will come together in the same way as 

 the anterior pillars to form a screen or curtain, which will shut off the. 



