THE ORGANS OF DIGESTION 



sheath of the muscles attached to it, through the submucous fibrous layer. On the under surface 

 of the organ, where it is thin and smooth, it can be traced on each side of the frenum through 

 the ducts of the submaxillary and the sublingual glands. As it passes over the borders of the 

 organ it gradually assumes a papillary character. That covering the under surface of the 

 organ is thin, smooth, and identical in structure with that lining the rest of the oral cavity. 

 The mucous membrane covering the tongue behind the foramen cecum and sulcus terminalis 

 is thick and freely movable over the subjacent parts. 



The mucosa consists of stratified squamous epithelial cells resting upon a basement mem- 

 brane, and this upon a papillated tunica propria of fibroelastic tissue containing the capillary 

 loops and nerves. Upon the apical two-thirds of the dorsum of the tongue the projections of 

 the mucosa are seen, and these are the papillae. They vary in number, size, form, and location; 

 they are the filiform papillae, fungiform papillae, and circumvallate papillae. 



EPIGLOTTIS. 



CIRCUM- 

 VALLATE 

 PAPILLC. 



FIG. 938. Upper surface of the tongue. 



The filiform or conical papillae (papillae filiformes) are small and scattered over the apical 

 two-thirds (dorsum and margin) of the tongue, and are arranged in parallel lines that are directed 

 outward and forward, especially posteriorly. Minute secondary papillae of a whitish color pro- 

 ject from these filiform structures. 



The fungiform papillae (papillae fungiformes) (Fig. 939) are scattered sparingly over the 

 dorsum of the tongue, and are more numerous at the sides and apex. They are larger in size 

 but less numerous than the preceding, and are readily recognized by their large size and deep 

 red color. Their bases are narrow and constricted, while the free ends are large and blunt; 

 the whole papilla is above the general epithelial surface of the tongue. These papillae possess 

 secondary papillae, and in their epithelium taste buds are at times seen. 



The circumvallate papillae (papillae vallatae) (Fig. 939) are of large size, but only eight to 

 twelve in number. They are arranged like a letter V at the junction of the apical two-thirds and 

 basal one-third of the dorsum, with the apex at the foramen cecum and the arms directed out- 



