TONGUE. 



1135 



materially the direction and shape of the 

 tongue : the styloglossi raise and expand the 

 sides, the palatoglossi raise and approximate 

 them, anil the hyoglossi depress them; the 

 one set makes the dorsum of the tongue 

 transversely concave, the other convex : 

 moreover, the posterior fibres of the genio- 

 glossus draw the centre of the tongue for- 

 wards and downwards, so that they also 

 render the tongue transversely concave. 

 The action of the genioglossus is peculiar ; 

 the most posterior fibres draw forwards 

 the base of the tongue, and are those chiefly 

 concerned in the protrusion of the organ ; 

 the most anterior concur in replacing the 

 tongue when thus protruded ; when the 

 whole muscle acts it compresses the tongue 

 into a sort of button, and carries it deep 

 down in the arch of the lower jaw. The 

 relations of the hyogiossus and genioglossus 

 are worthy of remark : they are congeners, 

 inasmuch as they both tend to draw the 

 tongue downwards ; they are antagonists, 

 inasmuch as the one tends to draw the tongue 

 principally forwards, the other principally 

 backwards; when all four muscles act, the 

 tongue is depressed deep in the jaw, but 

 further back than when the genioglossi act 

 alone ; when the two muscles of one side 

 act, that side alone is depressed, and a certain 

 torsion is given to the tongue which enables it 

 to [apply the tip advantageously to parts that 

 it would otherwise be very difficult to reach. 

 If the movement of the tongue in transferring 

 the tip from the last inferior molar tooth of 

 one side to that of the other be watched, with 

 the mouth open, at a glass, it will be seen to 

 be collected in a globe at the back of the 

 mouth, and to rotate horizontally, as it were 

 on a pivot. The only way in which I can 

 conceive this movement to be brought about, 

 is by the consentaneous action of the hyo- 

 glo.ssus of the one side with the genioglossus 

 of the other, the one right with the other 

 left, then the one left with the other right, 

 and so on, the styloglossi and palatoglossi 

 at the same time preventing the depression of 

 the tongue. 



But it would be vain to attempt to describe 

 in words the endless variety of movements 

 of which the tongue is susceptible ; and if it 

 were possible to give an idea of them, space 

 could not be afforded: so, dismissing this part 

 of my subject, I will proceed to the next. 



3. Tcgumentary system. The tegumentary 

 system of the tongue is formed by the mucous 

 membrane of the mouth passing on to it from 

 neighbouring parts, and undergoing special 

 modifications according to the part that it 

 invests. A superficial glance shows it at 

 once to admit of a triple division, into, first, 

 a really or apparently plane portion, situated 

 in front of the epiglottis, beneath the borders, 

 and on the free portion of the under surface ; 

 secondly, a papillary portion, covering the 

 anterior two-thirds of the upper surface, the 

 free borders, and the tip ; and, thirdly, a 

 glandular portion, occupying the posterior 

 third of the upper surface, where it is folded 



into little crypts and raised in nodules over 

 small mucous glands : these glands exist also 

 along the sides and beneath the tip : they will 

 be reserved for future description. 



The mucous membrane here, as elsewhere, 

 consists of three portions, a basement or 

 limitary membrane, underlaid by a submucous 

 areolar tissue, and surmounted by an epithe- 

 lium. 



a. Cutis. The sub-basement areolar tissue 

 of the tongue exists in sufficient quantity 

 and density to deserve the name of a true 

 chorion or cutis. It is thickest at the upper 

 surface, where it underlays the papillae, espe- 

 cially towards the median line; its density too 

 is the greatest here, sometimes amounting to 

 almost a cartilaginous hardness, and the pro- 

 portion of white fibrous tissue to the yellow 

 is the greatest; it is thinnest on the under 

 surface and edges, where it contains more oi 

 the elastic element, especially in the neigh- 

 bourhood of the epiglottis ; at the line where 

 the attached and free portions of the tongue 

 meet, it gradually merges off into the loose 

 elastic web that underlays the mucous surface 

 in these situations. Its inner surface receives 

 the insertion of all the intrinsic muscles of the 

 tongue, among which for a short distance it 

 dips, and it sends processes into the folds that 

 attach the tongue to neighbouring parts, as 

 the glosso-epiglottidean and fraenum. It is 

 the medium in which the nerves and vessels 

 destined to the surface break up previous to 

 their ultimate distribution : the vascular rami- 

 fications form a plane network, coincident with 

 the surface, from which, at regular intervals, 

 the papillary vessels ascend. 



b. The basement membrane is variously 

 modified in the three situations above indi- 

 cated; it is either continued plane, projected 

 into papilla?, or folded into mucous crypts, 

 from which its further involution constitutes 

 the minute ducts and ultimate follicles of the 

 mucous glands opening into these crypts : its 

 description will be involved in the particular 

 consideration of these structures. 



c. Epithelium. This very nearly approaches 

 in character the cuticle of the skin, which it 

 resembles in being of the scaly variety, in the 

 amount to which it exists, and in its being 

 divisible into two layers, a deep one closely 

 adherent to the basement membrane, consist- 

 ing of more recent cells, retaining much of the 

 cellular form (fig. 753., c.), and a superficial 

 one, readily desquamating, the cells of which 

 are older and flattened into scales (fg. 753., d.). 

 It exists in very different quantity in different 

 parts, being most abundant where it invests 

 the papillary structures. The shape of the in- 

 dividual cells is very various ; where they are 

 flattened their area is much extended (Jig. 753., 

 a.), and they look four or five times as large 

 as the deep-seated ones ; but probably there 

 is no increase in size, their lateral extension 

 resulting from their greater thinness: viewed 

 in profile they appear quite filamentary ; some 

 of them are not flattened but elongated, so 

 that they appear linear in all aspects, and are 

 really so. In spite of all these modifications 



