346 HEAD AND NECK 



was applied like a lid over the entrance to the vestibule of 

 the larynx. The investigations of Anderson Stuart have 

 shown that the superior aperture of the larynx is closed 

 during swallowing by the close apposition and the forward 

 projection of the two arytaenoid cartilages, which are forced 

 against the tubercle of the epiglottis. The muscles chiefly 

 concerned in that movement are the thyreo-arytaenoid muscles 

 and the transverse arytaenoid muscle. They form, collectively, 

 a true sphincter vestibuli. The ary-epiglottic muscles also 

 assist in the closure. 



THE TONGUE. 



The tongue is a mobile organ which lies on the floor of 

 the mouth. It consists of a mass of muscles covered with 

 mucous membrane, and interspaced with a small amount of 

 fat and some glands. It is closely associated with the 

 functions of taste, mastication, deglutition, and articulation. 



It has the form of a shoe turned upside down, and through 

 the opening of the shoe, which corresponds with the root of 

 the tongue, pass the muscles which connect the tongue with 

 the hyoid bone and the mandible (Figs. 131, 133). 



The free part of the tongue possesses a lower surface, and 

 a dorsum. The dorsum is separable into an oral or upper 

 portion, which is also called the upper surface and which ter- 

 minates anteriorly at the apex, and a posterior or pharyngeal 

 portion, which is also called the base. The lower surface, which 

 is smooth, rests on the floor of the mouth. The upper surface 

 is rough ; it lies in relation to the roof of the mouth (Figs. 

 72, no, and 114); the apex touches the incisor teeth, and 

 the base forms a part of the anterior wall of the pharynx 

 (Fig. no). The upper border of the base is continuous 

 with the upper surface and it forms the lower boundary of 

 the isthmus of the fauces. The upper surface is separated 

 from the lower surface, on each side, by a distinct but 

 rounded border (Fig. 134). 



The Mucous Membrane. The tongue is covered with 

 mucous membrane, which is continuous with the general 

 lining of the oral cavity and pharynx, but which presents very 

 different appearances on different areas of the tongue. In 

 the middle line of the tongue, at the junction of the upper 

 surface with the pharyngeal surface, there is a median pit in 



