500 SPECIAL PHYSIOLOGY. 



reaches from the apex to the base of the tongue, lying between the 

 hyo-glossus and the genio-hyo-glossus, blending anteriorly with the 

 fibres of the stylo glossus. Between the superior longitudinal and the 

 lingualis are placed the transverse fibres ; internally, these are con- 

 nected with the median fibrous septum, and, passing outwards, they 

 are inserted into the dorsum and margins of the tongue, where they 

 intersect the other muscular fibres. These transverse fibres form the 

 greater portion of the substance of the organ ; they are intermixed 

 with a considerable quantity of fat. 



From the varied course of its component fibres, the tongue pos- 

 sesses the power of movement in all directions. 



For the act of sucking, the tongue is especially important. The 

 lips of the infant being closely applied to the breast, the tongue is 

 drawn back, and the threatened vacuum in the mouth is filled with 

 milk, forced in by the atmospheric pressure on the breast, as well as 

 by the elasticity of the distended ducts of that organ. By means of 

 the palate, uvula, and posterior pillars of the fauces, the respiratory 

 passages through the nose and pharynx are shut off, so that air can- 

 not enter the mouth by that path, and, moreover, respiration is not 

 hindered until the act of swallowing takes place. Drinking, with the 

 lips closed on the rim of any vessel, involves a similar mechanism; 

 but the fluid is often allowed to enter the mouth by its gravity only. 

 In sipping, the fluid is drawn in by an inspiratory movement ; and, 

 most commonly, the act of drinking is performed partly by sipping, and 

 partly by pouring the fluid into the mouth. In drinking from a stream, 

 the lips are protruded and submerged, and a combination of sucking 

 with oral inspiration., takes place. 



Deglutition. 



Deglutition, or the act of swallowing, is that mechanical process by 

 which the food is passed from the mouth y through the opening called 

 the fauces, into the pharynx, and thence along the gullet, into the 

 stomach. This act is usually described as consisting of three stages : 

 first, that in which the food is forced backwards from the mouth, 

 through the fauces, into the pharynx ; secondly, that in which it is 

 made to traverse the middle and lower part of the pharynx to the 

 gullet ; and thirdly, that in which it descends along the gullet, and 

 enters the stomach. 



The first stage of deglutition is performed by aid of the tongue, the 

 hinder part of the hard palate and the soft palate, together with the so- 

 called pillars of, the fauces. The hard palate is formed by parts of the 

 superior maxillary and palate bones, covered by periosteum and a 

 dense mucous membrane. The soft palate descends, like an apron, 

 from the posterior border of the hard palate, and forms the upper mar- 

 gin and sides of the opening, seen on looking into the mouth, called 

 the fauces. The arched border of this opening, forming the isthmus 

 of the fauces, presents, in the middle line above, the pendulous body, 

 named the uvula. Two prominent ridges, on each side, are called the 

 pillars of the fauces ; the anterior pillars pass down on the sides of the 



