186 MOUTH DIGESTION. 



ished, deglutition is difficult and the sense of taste is markedly 

 deteriorated. 



Deglutition. This is the act of swallowing, and for purposes 

 of description is conveniently divided into three stages: 1. From 

 the mouth to the pharynx ; 2. Through the pharynx to the esoph- 

 agus ; and 3. Through the esophagus to the stomach. 



First Stage. The tongue is an organ composed of muscles, 

 some of which have their origin outside the tongue but end in it, 

 known as the extrinsic muscles, and others which are situated 

 wholly within the organ, and constitute its greater part ; these are 

 the intrinsic muscles. In the former group are the styloglossus, 

 hyoglossus, palatoglossus, and others ; and in the latter the 

 superior lingualis and inferior lingualis, together with others which 

 we need not name. For a detailed description of the muscles of 

 the tongue the reader is referred to anatomical text-books. The 

 floor of the mouth is made up of the two mylohyoid muscles, 

 which have their origin in the mylohyoid ridge and are inserted 

 into the hyoid bone. The digastric, stylohyoid, and geniohyoid 

 muscles need also to be mentioned in this connection. 



After the solid food has been thoroughly masticated and insali- 

 vated, it is collected by the tongue, aided by the cheeks, and 

 formed into a small mass, the alimentary bolus. This is placed 

 upon the dorsum of the tongue, which is then pressed against the 

 roof of the mouth by the action of the styloglossi and palatoglossi 

 muscles, thus carrying the bolus backward to the base of the 

 tongue. There is also contraction of the anterior belly of the 

 digastric, mylohyoid, and geniohyoid muscles, elevating and 

 moving forward the hyoid bone and the tongue, and the pharynx 

 and larynx are thus carried upward and under the bolus. The 

 bolus is now at the anterior pillars of the fauces, the palato- 

 glossi muscles covered with mucous membrane. The first stage 

 may now be considered to end and the second begin. Up to this 

 point the movement has been a voluntary one, absolutely under 

 the control of the will, for it would be possible at this point in 

 the process to eject the bolus from the mouth. It is probable, 

 however, that under ordinary circumstances the latter part of the 

 first stage is involuntary i. e., reflex as, indeed, are both the 

 second and the third stages throughout. 



The nerves which are involved in the first stage are the fifth 

 nerve, supplying the mucous membrane of the mouth and the an- 

 terior portion of the tongue ; and the glossopharyngeal, which is dis- 

 tributed to the posterior third of that organ. These are the sensory 

 nerves, or those which carry the aiferent impulses ; the motor 

 nerves are the hypoglossal, supplying the muscles of the tongue, 

 the mylohyoid branch of the inferior dental, the largest branch 

 of the inferior maxillary branch of the fifth, which supplies the 

 anterior belly of the digastric and the mylohyoid. 



