200 



ANATOMY OF VERTEBRATES. 



part; in a section anterior to the genioglossi the peripheral 

 layer is uninterrupted. The central mass consists of transverse 

 and vertical fibres, the latter not wholly intrinsic but partly 

 derived from the genioglossi : the peripheral mass mainly con- 

 sists of longitudinal fibres, 

 of which those along the 

 upper and under surfaces 

 are intrinsic, those on the 

 sides of the tongue in part 

 derived from the styloglossi. 

 As exemplified in the 

 plan, fig. 146, the vertical 

 and transverse fibres decus- 



Plan of intrinsic muscles of tongue. 00XU ^ ^ ^ ^^ ^ tf^ 



exclude the longitudinal fibres : the vertical ones diverge and 

 spread as they approach Z>, b, and cease near the margins a' ', a; 



the transverse also di- 

 verge, as they approach 

 Z>, Z>, and disappear near 

 the upper and under sur- 

 faces a, a. The vertical 

 emerge from the trans- 

 verse as they come near 

 the upper and under sur- 

 faces a, a, and the trans- 

 verse extend freely from 

 the vertical to attain the 

 lateral margins c, c. The 

 longitudinal fibres, which 

 appear as discs in trans- 

 verse section, fig. 147, c, are 

 seen near the periphery, 

 where the diverging ver- 

 tical and transverse fibres 

 leave room for them, as at 

 b, b, and in greater propor- 

 tion at the surfaces a a, cc. 

 Thus, at certain portions 

 of the tongue, three sets 

 of fibres traverse the same 

 area, in as many distinct 

 directions and at right angles one with the other ; the arrange- 

 ment being so that the crossing of the fibres of any two sets forms 



Section of cortical layer, upper part of tongue. 

 (30 diam.) ccxl. 



