THE MOUTH. 



407 



2-23. 



Theracemose glands (Fig. 221) are spread on the sides and base of the tongue. 

 Near its upper border they forui two rows, which are rendered visible by the 

 presence of a small tubercle placed beside each of them. At the base of the tongue 

 they are found beneath the fungiform and calyciform papillaB, as well as beneath 

 the layer of closed follicles which lines the isthmus of the fauces. 



At the entrance to this passage, the lingual mucous membrane is mammillated, 

 and each elevation has an oritice. This arrangement is connected with the 

 presence, at this part of the tongue, of the closed follicles (Figs. 222, 228), which 

 are more or less voluminous and aggregated, and separated from the muscles by 

 a continuous layer of racemose glands. They are composed of an envelope of 

 dense connective, and a mass of adenoid tissue, which has in its centre a 

 cavity that communicates with the orifice above the follicle, and is lined by the 

 lingual epithelium, minus its horny layer. 



4. Vessels and nerves. — The tongue is supplied with blood by two arteries, 

 the lingiud and sublingiml ; the blood is 

 removed by three large veins, two of which 

 enter the external tnaxillary, and the third 

 the intermd mamllari/ vein. The h/mphatics 

 constitute a very fine superficial network, 

 the emergent branches of which pass to 

 the submaxillary glands. The nerves are 

 the lingual, the glosso-pharyngeal, and 

 the great hypo-glossal ; the latter is a 

 motor nerve, and consequently supplies the 

 muscles ; the others are exclusively sensi- 

 tive, and are distributed more particularly 

 to the mucous membrane. 



Functions. — The tongue serves for 

 the prehension of liquids in all animals, 

 and for solid aliment in the Ox. It concurs, with the jaws, in propelling the 

 substances to l)e crushed between the molar teeth during mastication ; and 

 it is, besides, one of the essential organs of deglutition. It is able to play this 

 important and complex part, through the varied movements it can execute in the 

 interior of the mouth ; and the extent of these movements demands a moment's 

 notice. They are of two kinds : those which influence only the form of the 

 organ, and those which cause it to submit to various displacements. They result 

 in either compressing it from side to side, above to below, or curving it longi- 

 tudinally, and even transversely. These movements are principally, but not 

 exclusively, due to the action of the intrinsic fibres ; they are perfectly indepen- 

 dent of the movements which, as a whole, produce the total displacement of the 

 tongue. With regard to these latter, they may result in carrying the tongue 

 beyond the mouth, or withdrawing it into that cavity, inclining it to one side, 

 raising it against the palate, depressing it on the floor of the mouth, or, finally, 

 lifting it towards the pharynx. It is worthy of remark that these movements 

 do not alone result from the action of the proper lingual muscles above described ; 

 those belonging to the os hyoides, to which is attached the spur process, 

 concur also in producing them. But this process is not the only organ thus 

 attached to the hyoideal apparatus ; the larynx and, through it, the pharynx, are 

 placed in the same conditions, and are obliged to follow, Uke the tongue, the 

 movements of the bony framework supporting them. 



SECTION OF AN AMYGDALOID FOLLICLE 

 OF THE horse's TONGUE. 



1, Follicle cut through the middle ; 2, follicle 

 divided beyond its centre ; 3, section of a 

 racemose gland ; 4, vessel. 



