1140 



TONGUE. 



to be partly fibrous, partly granular : cer- 

 tainly something like yellow fibrous tissue 

 can be detected, particularly on the addition 

 of acetic acid ; but those specimens that I 

 have examined have appeared to be more 

 granular than fibrous, and in some cases, 

 where there has been a fortuitous rupture of 

 the papilla, there has been an abundant escape 

 of a finely granular material : the exact na- 

 ture of this granular material I have not been 

 able to ascertain ; it is not fatty. The me- 

 thod of termination of vessels is sufficiently 

 conspicuous, and has been already indicated. 

 With regard to the termination of nerves I 

 must confess, that, after long-continued and 

 careful search, I have been unable to find any 

 thing I can construe into a looped termina- 

 tion. I have traced the nerve for some little 

 way into the simple papilla, and then, its out- 

 line becoming less and less definite, it has 

 ceased to be visible, apparently from the loss 

 of the strong refraction of the white substance 

 of Schwann. If I might hazard an opinion, I 

 should say that the axis was probably de- 

 nuded of this investment, and, thus laid bare, 

 underwent some specific peripheral modifi- 

 cation. In a paper by Dr. Waller, recently 

 published in the" Philosophical Transactions 

 of the Royal Society," a method of nervous 

 termination by open months is suggested : con- 

 sidering the solid nature of the nerve-axis, this 

 appears to be an opinion that requires either 

 some modification, or the confirmation of re- 

 peated and varied observations, before it can 

 be received as certain. At present our means 

 of examining the termination of nerves, either 

 in the organs of sense or elsewhere, are im- 

 perfect, and until they are less so we can hope 

 to make but little advance in this, at present, 

 obscure subject. 



Functions of the different papillcs. Three 

 offices are to be discharged by the papilla? 

 thev are to exercise the sense of taste, the 

 sense of touch, and to form a suitable cloth- 

 ing and protection to the tongue. The struc- 

 ture of the circumvallate and fungiform pa- 

 pilla?, their shape, their position, the nature 

 of their epithelium, all point them out as the 

 organs that are to discharge the first-men- 

 tioned function, and their nervous supply, 

 which may be demonstrated with facility, 

 makes that probability a certainty. To detail 

 the evidence on which this conclusion is based 

 would merely be to repeat what the reader 

 will find given at length under the "articles 

 FIFTH NERVE, EIGHTH NERVE, and TASTE, 

 to which I therefore refer him. By what pa- 

 pillac.then, is the sense of touch exercised ? I 

 think by the conical, and by them in contradis- 

 tinction to their non-gustatory congeners, the 

 filiform. My reasons are, first, that the sense 

 of touch is only possessed in any perfection by 

 the papillae at. the tip of the tongue.* Now 



* There can be no doubt about this fact ; and it 

 is what we might antecedently expect, because it 

 is the most movable part, and therefore has the 

 widest range of application ; because it is the most 

 capable of movement, and therefore the best adapted 

 for that which is an essential condition of touch ; 



these are conical and of the form the'most re- 

 moved from the filiform tvpe, that is, their 

 epithelium is the least abundant of all the non- 

 gustatory papilla?. Secondly, because the struc- 

 ture or the filiform papillae is the most incompat- 

 ible that could be devised for the possession of a 

 sense of touch in any perfection. And, thirdly, 

 because we do find, in fact, that the centre of 

 the dorsum of the tongue, where the filiform 

 papillae exist in the greatest abundance, is the 

 least sensitive part of any. Therefore, unless 

 we assign the sense of touch to the gustatory 

 papillae, which the lowness of its conditional 

 the back of the tongue, where the gustatory 

 papillae are so abundantly developed, seems to 

 negative, we are driven to the conical as the 

 only ones that can possess it. The filiform 

 papilla? remain for the third office that of 

 clothing and protecting the exposed dorsum 

 of the tongue ; their pilose investment ad- 

 mirably adapts them for this, and at the same 

 time it imparts to the surface a certain pre- 

 hensile power, enabling it to take hold of 

 and move readily what is placed on it, while 

 the backward direction of the hairs adds yet 

 more a special facility for transmitting food 

 towards the pharynx. 



Mucous glands. These are largest and most 

 abundant at the base of the tongue, where 

 they occupy the space behind the circum- 

 vallate papilla?, and lie immediately beneath 

 the surface, which they raise in nodular emi- 

 nences. The most antfrior of them form a 

 V-shaped ridge, the counterpart of that formed 

 by the circumvallate papillae, from which they 

 are separated by a corresponding furrow. 

 These structures, which are true mucous 

 glands, analogous to the buccal and labial, 

 are of an oval or roundish lenticular shape : 

 in front of the epiglottis they are gradually 

 lost. Each gland is surmounted by a distinct 

 orifice, most conspicuous in the most posterior 

 of them, opening into a little crypt, generally 

 closed and collapsed, but dilatable so as to 

 be large enough to contain a mustard-seed, 

 and into the bottom of these crypts the 

 minute ducts of the glands open. Some of 

 these crypts I have found extending into 

 long and capacious canals, branching in dif- 

 ferent directions, and undermining the surface. 

 I have traced some of them half or three- 

 quarters of an inch before they have termi- 

 nated in their blind extremities : their surface 

 is quite smooth, and the orifices of the ducts 

 of neighbouring glands might be seen tenni- 



O ~ O ~ 



nating in different parts of it. They probably 

 act as reservoirs, and permit some accumula- 

 tion of the secretion, and also prevent the 

 orifices of the glands from infarction by the 

 matters passing over the surface. Similar 

 glands, but smaller, are seen along the sides 

 of the tongue, particularly near the base ; and 

 under the tip a small aggregation of them, 



because we find it is the tip that we do apply to 

 parts that we want to feel ; because the tip is capa- 

 ble of receiving a pointed form, and therefore loca- 

 lising the impression more perfectly ; and because 

 the tip receives the most abundant supply of twigs 

 from the fifth nerve. 



