TONGUE. 



J127 



and inferior must be to some extent arbitrary : 

 however, most of those on the upper surface 

 are intrinsic in their origin, those at the sides 

 are extrinsic in their origin, while those on 

 the inferior surface are sufficiently individual 

 and distinct : some subdivision appears ne- 

 cessary, and the one adopted will at any rate 

 assist in remembering these facts. 



The microscopical examination oftliin sections. 

 On making a thin transverse vertical section 



of the human tongue, and examining it with 



the microscope*, we sec that the appearances 

 indicated by a similar section, viewed with the 

 naked eye, are correct, namely, that the in- 

 trinsic muscular fibres assume three principal 

 directions, a vertical, a transverse, and a lon- 

 gitudinal ; and that the longitudinal are con- 

 fined to the neighbourhood of the surface. 

 But we see more; we see a very curious and 

 artificial arrangement of the fibres very much 

 contributing to facilitate their package, and by 

 which they mutually support one another 



Fig. 748. 



Transverse vertical section of the left half of the human tongue at the most posterior part of the free 



portion. (Magnified 10 diameters.) 



a, a, cutis ; b, I, cortical portion, consisting of the three orders of fibres ; c, central portion, con- 

 sisting only of two ; d, discs of longitudinal fibres, seen in section ; /, horizontal median plane ; 

 g, line of emergence of the vertical from the transverse fibres ; i, i', the most superior and inferior 

 of the transverse curving up and down ; k, k, the most lateral of the vertical curving outwards. 



* The best method to adopt in making these 

 investigations is to keep a fresh human tongue two 

 or three days in spirit, and then boil it about an 

 hour. On being first put into the boiling water it 

 contracts and becomes very hard. \Vhen sufficiently 

 boiled, let it dry in the air for a day, and then make 



the sections with some very thin flat knife. Place 

 the sections on a glass slide with a drop or two of 

 water, cover them with a piece of thin glass, and 

 view them with an inch, or, if a very large field 

 is wanted, a two-inch object-glass. 



4 c 4 



