TONGUE. 



1129 



longest ; hence we see the fasciculi in these 

 situations much larger and more densely 

 packed than in the intermediate positions, 

 so that they more than equal the longi- 

 tudinal fibres that they transmit. The ex- 

 treme lateral fibres, on the other hand, that 

 spread out and interlace, having little more 

 for their office than to support the longitudi- 

 nal fibres, are very small and scanty, many of 

 them consisting of only a single fibre, and 

 hence at these points the preponderance of 

 the longitudinal over the vertical and hori- 

 zontal fibres is the greatest. Fifthly, the most 

 deep-seated of the longitudinal fibres of the 

 upper and under surface are underlaid by a 

 definite floor of transverse fibres, and simi- 

 larly the deepest of those at the side are under- 

 laid by a floor of vertical fibres; therefore in 

 these situations there is a strong line of de- 

 marcation, the discs are abundant down to the 

 bottom of the cortical layer, and there they 

 terminate suddenly (fig. 751.); but in the in- 

 termediate positions there is no definite floor, 

 no line of demarcation, but the discs of lon- 

 gitudinal fibres dip down at irregular distances 

 (figs. 748, 749, 750.). 



This is the general plan and rationale of the 

 arrangement, but it is rather an exposition 

 than a description, and it must be understood 

 as merely referring to a transverse vertical 

 section of the tongue, made at the most pos- 

 terior part of the free portion of the tongue : 

 there are often irregularities that make it 

 difficult tc recognise the plan, and, in some 

 situations, certain disturbing forces, and su- 

 peradded parts that quite upset its symmetry. 

 For example, behind the anterior third of the 

 tongue, the genioglossus is seen entering 

 its inferior surface, and displacing all longi- 

 tudinal fibres (fig. 747. d) ; further back, 

 this displacement is more considerable, and 

 we have similar infringements from other 

 muscles; and the intermixture of fat towards 

 the base of the tongue tends materially to 

 upset the regularity of the muscular arrange- 

 ment. Yet, in spite of this, it may always be 

 detected, and the average of appearances will 

 be such as I have described. 



The muscular fibres are neither straight 

 nor parallel ; those of each system maintain 

 their general direction, but their course is 

 wavy and tortuous, and characterised by the 

 utmost irregularity ; as the fibres pass out- 

 wards they branch and sometimes re-unite 

 (figs. 750, 751.), though their branchings are 

 much more frequent than their re-unions, 

 and hence the fasciculi are smaller and more 

 numerous near the periphery than towards 

 the centre (fig. 751.) ; by these branchings of 

 the fasciculi each set of fibres, the vertical 

 or transverse, possesses what may be called 

 an intrinsic network, imperfectly marked cer- 

 tainly, but sufficient in some parts to mask 

 their parallelism and to break up the rows of 

 longitudinal fibres that are packed between 

 them. 



The number of fibres in each of the vertical 

 or transverse fasciculi, varies according to the 

 part of the section viewed, and the situation 



in the tongue irom which it is taken ; some- 

 times one single fibre constitutes the fasci- 

 culus, if one may say so, sometimes many 

 dozen. Some of the largest are the most 

 superior of the horizontal, those that curve 

 up on each side towards the upper surface 

 (fig. 750.). The same variety of size exists in 



Fig. 750. 



li 



a. 



Portion of cortical layer of the right supra-lateral 

 region of the tongue, showing the interlacement of 

 a, , the horizontal with b, b, the vertical fibres, the 

 longitudinal fibres filling the intervals having been 

 removed. Magnified 30 diameters. 



the discs of longitudinal fibres cut across; the 

 number of fibres in them may be counted, 

 from two or three to thirty or forty : those 

 nearest the surface are certainly the smallest, 

 and they do not completely fill the meshes of 

 the muscular network through which they pass 

 (fig. 751.), but a certain quantity of fibrous 

 tissue dips down among them : this, however, 

 only for a little way. The shape of the longi- 

 tudinal bundles is as various as their size 

 circular, polygonal, triangular, elliptical, in 

 fact, every conceivable shape (fig. 751.); they 

 seem moulded by the fibres among which 

 they lie, or, more correctly, they and the 

 others among which they lie, mutually regu- 

 late each other's shape and direction. 



The peculiarity, then, of the arrangement of 

 the intrinsic muscles of the tongue is this : 

 that there are three sets of fibres passing 

 through the same area, and acting in three 

 different directions ; that these three direc- 

 tions are, in the main, at right angles the one 

 to the other, in fact, that they coincide with 



