TONGUE. 



1131 



ing towards the centre, where they finally meet, 

 and then the central part of the tongue is con- 

 stituted in the same way as it is throughout 

 the whole succeeding length of the organ, 

 namely, by decussating vertical and transverse 

 fibres ; but as yet no longitudinal fibres have 

 appeared, and they are not seen till after the 

 transverse area of the tongue has been 

 entirely occupied by the vertical and hori- 

 zontal fibres as above described. They first 

 appear at the inferior surface, then at the 

 sublateral and lateral regions ; next they are 

 seen at the centre of the upper surface in a 

 small definite cluster, from which they spread 

 out, and so complete the circumference of the 

 tongue. 



We see from this that the fibres that occupy 

 the extreme point of the tongue are the 

 transverse ; that the next met with are the 

 vertical ; and that the longitudinal do not 

 extend so far forward as either of the other 

 two. This is what might be expected. The 

 chief muscular, requisition at the extremity 

 of the tongue is the power of pointing it : 

 the shape of a tactile part is eminently 

 subservient to its power of touch, because 

 exact localisation, which is a most impor- 

 tant element in touch (if it is not the very 

 essence of it), depends on the smallness 

 of the touching part. Now the extremity of 

 the tongue, of its ordinary broad, flat shape 

 when at rest, would be a very poor tactile 

 instrument, and very far removed from a form 

 that would capacitate it for the minute ap- 

 preciation of distance and form. In what 

 way, then, is the desired pointed shape of the 

 tip of the tongue to be produced ? Manifestly 

 by transverse contraction, for it is by the 

 spread of the tongue in this direction that it 

 departs from the pointed form ; and so we see 

 the transverse fibres continued beyond either 

 of the others, and occupying at the extreme 

 tip the whole of the space assigned to the 

 muscular structure. Furthermore, the longi- 

 tudinal fibres are not necessary at the extreme 

 point, either to flatten or shorten the tip, 

 which is brought about by its own elasticity 

 immediately on the cessation of the con- 

 traction of the transverse fibres, or to move it 

 in any direction, which is done rather by the 

 movements of the parts coming immediately 

 next the tip than of the tip itself. Thus, both 

 negatively and positively, we see a reason 

 for the continuation of the transverse fibres 

 further forwards than either of the other two 

 sets. 



The section last described completes what 

 may be called the theoretical structure of the 

 tongue (it is shown in jig. 748., in one half of 

 its extent) : the next change is one of in- 

 fraction of that completeness of muscular 

 structure, occasioned by the entrance of the 

 genioglossi muscles on the inferior surface, 

 whereby the continuity of the cortical layer is 

 isolated, there being no discs in the space 

 occupied by the immergence of these two mus- 

 cles. The subsequent changes in the appear- 

 ance of successive sections, are just such as 

 might be expected from the description al- 



ready given of such sections when viewed by 

 the naked eye ; therefore, for the sake of 

 brevity, I shall not here advert to them. 



A longitudinal vertical section, of course, 

 displays a reversing of the position in which 

 the discs and profile interlacement are re- 

 spectively seen ; the discs are here in the 

 central part instead of in the cortical, being 

 the transverse fibres cut across ; the cortical 

 layer is free from discs (except where, from 

 the vertical and longitudinal fibres being ob- 

 lique, they are obliquely cut), and is occupied 

 by the longitudinal and vertical fibres, both 

 seen in profile. 



A horizontal section displays very much the 

 same appearance as the last : the discs are in 

 the central part, and there is an absence of 

 them in the circumferential portion; but in 

 this case the discs are of the vertical fibres, in 

 the other they were of the transverse. 



Superficial sections, or sections made ob- 

 liquely, I shall not attempt to describe; by 

 such means the appearances might be in- 

 finitely varied, but their description would 

 merely tend to confusion. 



From the above account it is seen that the 

 microscopical investigation of the subject not 

 only confirms and proves the conclusion ar- 

 rived at by other means, but adds many new 

 and interesting facts, and supplies us with one 

 more instance of that contrivance and adapta- 

 tion of means to end that meets us at every 

 point. 



I have entered rather fully into the intrinsic 

 muscular arrangements of the tongue, because 

 there is no good account of the subject, that 

 I can find, in the English language, nor of the 

 appearances as seen by the microscope, in any 

 language ; and I considered such an account 

 a desideratum. 



Mode of termination of the intrinsic fibres. 

 All the intrinsic fibres of the tongue, and 

 indeed, it may be said, almost if not quite all 

 of the extrinsic too, terminate by becoming in 

 serted into the cutis the sub-mucous fibrou. 

 tissue which is extremely dense and thick, 

 particularly on the upper surface. The trans- 

 verse and vertical fibres pass direct to the 

 cutis ; the longitudinal all ultimately have a 

 similar insertion. In vertical sections the fibres 

 may be seen passing up or down to the sur- 

 face, and entering the cutis, which having 

 pierced for a certain extent, they terminate : 

 some of them end just as they enter the fibrous 

 tissue ; some of them may be traced quite up 

 to the papilla3. 



It might naturally be expected that the 

 muscular fibres of the tongue would, from 

 their isolation, present great facilities for see- 

 ing the mode of the termination of muscle in 

 fibrous tissue ; and indeed this is the case in 

 a remarkable degree ; they seem to furnish the 

 great desideratum of a natural isolation of the 

 individual fibres, at the point where you are 

 sure of seeing their union with the fibrous 

 tissue that forms their means of attachment. 

 As the opinions that I have come to from my 

 own observations differ from those that are 

 the result of some of the best researches on 



