340 THE DIGESTIVE APFABATUS IN MAMMALIA. 



orifice. This arrangement is connected with the presence, at this part of 

 the tongue, of the closed follicles, which are more or less voluminous and 

 aggregated, and separated from the muscles by a continuous layer of race- 

 mose glands. They are composed of a casing of condensed 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 lingual and sublingual; the blood is removed by three large 

 veins, two of wHch enter the external maxillary, and the third the internal 

 maxillary vein. The lymphatios constitute a very fine superficial network, 

 whose emergent branches 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 sensitive, and are distributed more particularly to the mucous 

 membrane. 



Fdnotions. — The tongue serves for the prehension of liquids in all 

 animals, and for solid aliment in the Ox. It concurs, with the jaws, in pro- 

 pelling the substances to be crushed between the molar teeth during masti- 

 cation ; 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 move- 

 ments 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 longitudinally, and even transversely. 

 These movements are principally, but not exclusively, due to the action of 

 the intrinsic fibres ; they are perfectly independent 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 intermaxillary space or, finally, 

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

 ments 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 lingual appendix, concur also in producing them. But this appendix is 

 not the only organ thus attached to the hyoideal apparatus ; the larynx and, 

 through its intermediation, the pharynx, are placed in the same conditionsj 

 and are obliged to follow, like the tongue, the movements of the bony frame- 

 work supporting them. 



There consequently results between these three organs a remarkable 

 unity of action, which is readily explained by the part they all take in the 

 one common act of deglutition. 



5. Soft Palate. (Figs. 148, 152.) 



Preparation. — ^Tlie soft palate is studied: 1, On the antero-posterior and vertical 

 section of the head (fig. 152); 2, On the portion intended to show the interior of the 

 pharynx (see the preparation of this region) ; 3, On the portion represented in fig. 148, 

 the mode of dissecting which has been indicated at page 333 ; in removing the mucous 

 membrane and glandular layer, the fibrous membrane and the two intrinsic muscles are 

 exposed. The extrinsic muscles should be studied with those of tlie pharynx. 



Situation — Form. — The soft palate (jpalatum molle, velum pendulum palati) 

 is suspended like a partition between the mouth and the pharynx, aiud by its 



