THE LINGUAL REGION. 



417 



The extrinsic muscles of the tongue are those which have their origin external, 

 and only their terminal fibres contained in the substance of the organ. They are : 

 the Stylo-glossus, the Hyo-glossus, the Palato-glossus, the Genio-hyo-glossus, and 

 part of the Superior constrictor of the pharynx (Pharyngeo-glossus). The intrinsic 

 are those which are contained entirely within the tongue, and form the greater 

 part of its muscular structure. 



The tongue consists of symmetrical halves separated from each other in the 

 middle line by a fibrous septum. Each half is composed of muscular fibres 

 arranged in various directions, containing much interposed fat and supplied by 

 vessels and nerves. 



To demonstrate the various fibres of the tongue, the organ should be sub- 

 jected to prolonged boiling, in order to soften the connective tissue; the dis- 

 section may then be commenced from the dorsum (Fig. 280). Immediately 

 beneath the mucous membrane is a submucous, fibrous layer, into which the 

 muscular fibres which terminate on the surface of the tongue are inserted. 



Upon removing this, with the mucous mem- 

 brane, the first stratum of muscular fibres is 

 exposed. This belongs to the group of intrin- 

 sic muscles, and has been named the Superior 

 lingualis. It consists of a thin layer of 



Cut edge of Superficial lingualis. 



FIG. 280. Muscles on the dorsum of the 

 tongue. 



FIG. 281. Coronal section of tongue. Showing intrinsic 

 muscles. (Altered from Krause.) a, lingual artery : b, Inferior 

 lingualis, cut through ; c, fibres of Hyo-glossus ; d, oblique fibres 

 of stylo-glossus; e, insertion of Transverse lingualis; /, Supe- 

 rior lingualis ; g, papillae to tongue ; h, vertical fibres of Gemo- 

 hyo-glossus intersecting Transverse lingualis ; i, septum. 



oblique and longitudinal fibres which arise from the submucous fibrous layer, close 

 to the Epiglottis, and from the fibrous septum, and pass forward and outward to 

 the edges of the tongue. Between its fibres pass some vertical fibres derived from 

 the Genio-hyo-glossus and from the vertical intrinsic muscle, which will be described 

 later on. Beneath this layer is the second stratum of muscular fibres, derived prin- 

 cipally from the extrinsic muscles. In front it is formed by the fibres derived from 

 the Stylo-glossus, running along the side of the tongue, and sending one set of fibres 

 over the dorsum which runs obliquely forward and inward to the middle line, and 

 another set of fibres, seen at a later period of the dissection, on to the under surface 

 of the sides of the anterior part of the tongue, which run forward and inward, 

 between the fibres of the Hyo-glossus, to the middle line. Behind this layer of 

 fibres, derived from the Stylo-glossus, are fibres derived from the Hyo-glossus, 

 assisted by some few fibres of the Palato-glossus. The Hyo-glossus, entering the 

 side of the under surface of the tongue, between the Stylo-glossus and Inferior lin- 



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