170 



HAND-BOOK OF PHYSIOLOGY. 



nence than those of the skin is due to their interspaces not being filled 

 up with epithelium, as the interspaces of the papillae of the skin are. 

 The papillae of the tongue present several diversities of form; but three 

 principal varieties, differing both in seat and general characters, may 

 usually be distinguished, namely, the (1) circumvallate, the (2) fungi- 

 form, and the (3) filiform papillae. Essentially these have all of them 



lae 



FIG. 349. Papillar surf ace of the tongue, with the fauces and tonsils. 1,1, circumvallate papil- 

 , in front of 2, the foramen caecum ; 3, f ungif orm papillae ; 4, filiform and conical papillae ; 5, trans- 

 verse and oblicme rugae; 6, mucous glands at the base of the tongue and in the fauces; 7, tonsils; 8, 

 part of the epiglottis; 9, median glosso-epiglottidean fold (frsenum epiglottidis). (From Sappey.) 



the same structure, that is to say, they are all formed by a projection of 

 the mucous membrane, and contain special branches of blood-vessels and 

 nerves. In details of structure, however, they differ considerably one 

 from another. 



The surface of each kind is studded by minute conical processes of 

 mucous membrane, which thus form secondary papillae. 



