1130 



the three axes of the cube ; that to facilitate 

 this arrangement, a beautiful system of pack- 



Fig. 751. 



TONGUE. 



Cortical layer from upper surface. (Magnified 

 30 diameters/) 



a, vertical fibres; b, topmost stratum of the 

 horizontal ; c, longitudinal, in section, occupying 

 the interspaces between the vertical. 



age is adopted, whereby each of these is 

 enabled to pass in a straight line to its destin- 

 ation without being interfered with by the 

 other two ; whereby the individual bundles 

 of each set are isolated from their fellows ; 

 whereby the whole of them are contained in 

 the smallest possible compass ; whereby they 

 not only admit the passage of, but mutually 

 support and conduct each other ; whereby, in 

 consequence of this, they are enabled to dis- 

 pense with the support of cellular tissue, 

 which accordingly we find absent ; whereby, 

 lastly, the tongue contains the greatest amount 

 of muscular tissue possible for its bulk. This 

 system of package consists of this that the 

 crossing of the fibres of any two sets forms 

 a lattice work, or mesh, through which the 

 third shall pass, and that the successive layers 

 of the crossing fibres shall be so arranged 

 that the areolae shall form continuous channels 

 for the transmission of the perforating ones. 

 In whatever plane we look at the fibres, we 

 find that this is the case that two sets are 

 crossing fibres and one set perforating that 

 two are seen in profile, one in section ; but, 

 as we vary the plane, so do we vary the ap- 

 pearance of the fibres, one set alone remain- 

 ing the same and two interchanging. Thus, 

 in a transverse vertical section the transverse 



and vertical fibres are seen in profile, and the 

 longitudinal in section ; in a longitudinal ver- 

 tical section the vertical and longitudinal are 

 in profile, and the transverse in section j while 

 again, in the horizontal section, the trans- 

 verse and longitudinal are seen in profile, and 

 the vertical in section. So, no set can be 

 called a perforating set or a crossing set, 

 they are all equally so. 



Again, we see that the office of the longi- 

 tudinal fibres requires that they should have 

 that special superficial arrangement which is 

 the only one left them by the necessary dis- 

 position of the other two. The chief office of 

 the longitudinal fibres is to alter the direction 

 of the tongue longitudinally, to twist it from 

 side to side, or up and down ; any thing but 

 a superficial distribution would render them 

 powerless for this act. For if the longitu- 

 dinal fibres were placed in the centre, it is 

 evident that they could only shorten the 

 tongue; but, being arranged superficially, when 

 a portion of them contracts, that side of the 

 tongue on which the contracting ones are is 

 shortened more than the rest ; in other words, 

 the tongue is turned towards that side ; and 

 it is only when the whole sheath of longi- 

 tudinal fibres acts equally that the tongue is 

 contracted directly backwards. 



Having premised this general description, 

 I shall now proceed to give a particular ac- 

 count of the microscopical appearances of 

 successive sections made in the three prin- 

 cipal planes the transverse, the longitudinal, 

 and the horizontal. I shall begin with the 

 transverse as being the clearest and the most 

 illustrative. 



The first transverse vertical sections, made 

 at the tip of the tongue, of course remove 

 successive portions of the papillary structure : 

 we next come to the cuds the dense areolar 

 tissue subtending the papilla? and many 

 sections are made before the appearance of 

 any muscle ; we have in fact to get through 

 the thickness of the cutis. The first muscular 

 fibres that make their appearance are the 

 transverse, consisting of a single slender 

 bundle of fibres in that direction, occupying 

 nearly a middle plane between the upper and 

 under surfaces, lying horizontally, collected 

 into a single bundle in the centre, but breaking 

 up at each end into smaller fasciculi, which 

 diverge as they pass to their insertion into 

 the cutis at the sides of the tongue, so as to 

 gain a more extended attachment. The 

 sections following this display an increasing 

 quantity of this muscle, the diameter of the 

 unbroken bundle in the centre being greater, 

 and .the fasciculi into which it divides at 

 the sides more numerous ; but as yet no 

 other system of fibres has appeared. The 

 next addition, as we proceed backwards, is 

 that of vertical fibres, which are at first very 

 few and scanty, and placed not in the centre, 

 but in two sets, one on each side of the 

 centre ; they converge a little as they pass 

 upwards, and are rather curved, presenting their 

 concavity outwards. The succeeding sections 

 show them increasing in numbers and spread- 



