THE ORAL CAVITY 161 



of limited movement. In snakes tlie ton^ne is a slender l)ifurcate 

 muscular orfjan that is usually retractable within a sheath in the 

 base of the mouth. It is covered with stratified squamous ei)ithe- 

 lium, below which a thin coat of coimective tissue with chromato- 

 phores adjoins the underlying- muscles. The majority of the 

 muscle fibers run longitudinally. The main blood vessels and the 

 large nerve trunks run through the center of the tongue on either 

 side of a median band of peri)en<licular muscle. It a])parently 

 functions as an olfactory receptor in snakes. 



The mammalian tongue is an active organ com])osed, in greater 

 part, of voluntary muscle sheathed ])y a mucous membrane con- 

 tinuous with that of the mouth and pharynx. Extrinsic muscles 

 enter the tongue posteriorly and connect it with the cartilages of 

 the throat. The body of the tongue is com])osed of the intrinsic 

 muscle, or tongue nuiscle proper, which is directly concerned with 

 the mo\ements of the tongue. 



A vertical partition, the median or lingual septum, of dense fibro- 

 elastic connective tissue extends from the lower to the upper sur- 

 faces and from the base to the tip dividing the tongue into two equal 

 lateral portions. Small bundles of muscle fibers of the skeletal 

 type are arranged longitudinally, vertically, and transversely, and 

 cross each other at right angles. The muscle fibers and bundles 

 are sej^arated from each other by thin sheets of fibroelastic and 

 adipose connective tissues in varying amounts. 



Between the muscular portion of the tongue and the epithelial 

 sheath there is a narrow region of subepithelial connective tissue 

 from the surface of which projections extend into the overlying 

 epithelium. This connective tissue is continuous with the con- 

 nective tissue separating the muscles of the tongue ])roper. 



The epithelium of the mucosa of the tongue is of the stratified 

 squamous type throughout. The surface is smooth for the most 

 part along the sides and on the ventral surface and is similar to 

 the lining of the mouth with which it is continuous. The two- 

 thirds toward the tip is roughened by papillae of varying sizes and 

 shapes (Fig. 100), formed by upward projections of the subepithelial 

 connective tissue that carry with them a co\ering of stratified 

 squamous epithelium. The anterior region of the dorsal surface of 

 the tongue bearing them is called the papillary portion. The 

 posterior third of the tongue may lack papilke of any kind, but may 

 have lymphoid tissue forming masses called the lingual tonsils 

 beneath the superficial mucous membrane. 

 11 



