I 4 2 



NORMAL HISTOLOGY. 



THE TONGUE. 



The tongue is essentially a complex mass of striped muscle, the free 

 surfaces of which are covered by an extension of the mucous membrane 

 lining the mouth and the pharynx. 



The muscles of the tongue include two groups, the extrinsic and the 

 intrinsic. The former (the genio-glossus, the hyo-glossus, the stylo-glossus 

 and the palato-glossus) are all paired and extend from the skull or the hyoid 

 bone to the tongue; the latter comprise the particular muscle, the lingualis, 

 forming the chief mass of the organ. The tongue is incompletely divided 

 into symmetrical halves by a vertical partition of dense connective tissue, the 

 septum lingua, which extends from the hyoid bone behind to the tip of the 

 tongue but fades away before reaching the apex. It is much better developed 

 in the middle third of the tongue than at the ends, but even here the septum 



Longitudinal fibres 



Glands 



Portion of sublingual gland 



'. > ^*- 



Septum Genio-glossus Hyo-glossus 



FIG. 181. Transverse section of child's tongue, through middle third. X 3. 



falls short of the dorsal mucous membrane by a few millimeters. On viewing 

 with low magnification a cross-section of the tongue at its middle third 

 (Fig. 181), the intricate feltwork of muscle-fibres is seen to comprise fibres 

 running in three general directions longitudinal, vertical and transverse. 

 The longitudinal fibres appear transversely sectioned and form a well-marked 

 superficial or cortical layer, some 5 mm. thick, immediately beneath the 

 scanty submucous tissue covering the dorsum. These fibres include the 

 principal part of the lingualis muscle, supplemented by fibres from the stylo- 

 glossus. The vertical fibres, most conspicuous as the deeply placed and 

 obliquely cut masses of the genio-glossus on either side of the septum, 

 radiate towards the dorsal surface, where the lingual bundles end in the sub- 

 mucous layer. The transverse fibres are entirely from the lingualis, with the 

 exception of those contributed by the palato-glossus. They arise from the 

 septum and interlace with the vertical and longitudinal bundles; on approach- 

 ing the mucosa, they break up into strands which find their way between 

 the superficial longitudinal fibres to a submucous insertion. Branching is a 

 peculiarity exhibited by many muscle-fibres that end in the submucosa. 



The mucous membrane of the tongue corresponds in general structure 

 with that lining the adjacent surfaces of the mouth and pharynx in consisting 

 of the epithelium, the tunica propria and the submucous layer. Over the 



