888 ORGANS OF SPECIAL SENSE 



A fibrous septum separates the halves of the tongue and extends in the middle 

 plane from base to apex; and a strong fibrous membrane, the hypoglossal mem- 

 brane, passes from l)eneath the l>ase of the tongue to the body of tlie liyoid bone. 



The Muscles of the Tongue. — The muselesdf the tongue are both extrinsic, 

 and special or intrinsic. 



The extrinsic muscles are the hyo-glossus, genio-hyo-glossus, stylo-glossus, 

 palato-glossus, and a small part of the superior constrictor. (For extrinsic mus- 

 cles of tongue see pages 451-454. ) 



The intrinsic muscles. — The lingualis superior constitutes a superficial 

 longitudinal stratum, which extends from the liase to the tip of the organ, imme- 

 diately beneath the mucous membrane. The fil)res form short fascicles attached to 

 the overlying tissues, and are placed between the hyo- and stylo-glossi muscles of 

 the opposite sides of the tongue, both pairs of which, near the base, overlap the 

 fibres of the lingualis. 



The inferior lingualis is composed of two bands which reach from the base to 

 the apex on the under surface of the tongue. Posteriorly some of the fibres become 

 attached to the body of the hyoid bone. Each of these bands is placed between 

 the hyo- and genio-hyo-glossus, and near the tip some of its fibres mix Avith those 

 of the stylo-glossus muscle. 



The transverse fibres mixed with fat lie l:)etween the two muscles just de- 

 scriljed, and form a considerable part of the bulk of the tongue. Tliey take origin 

 from the luedian fibrous septum, and, curving outwards and upwards, are inserted 

 into the sides and dorsum of the organ. 



The vertical fibres decussate with the transverse, and pass from the dorsum to 

 tlie under surface of the tongue in curves with their concavities looking outwards. 

 The fi1>res become shorter as they approach the margin of the tongue. 



Arteries. — The arteries are derived from the lingual, facial, and ascending 

 pharyngeal. 



Nerves. — The nerves are — the lingual branch of the mandibular division of 

 the fifth, which supplies the papillae of the fore part and sides of the tongue; the 

 lingual branch of the glosso-pharyngeal, which supplies the base and sides, in- 

 cluding the circumvallate papilla'; the fine branches from the superior laryngeal, 

 which reach the root close to the epiglottis, and a lingual branch from the facial 

 (Testut). 



The hypoglossal supplies the muscular substance of the tongue, as well as most 

 of the extrinsic muscles; and the chorda tympahi'IHi-ouglV the facial contributes 

 also some filaments. ^ ./ 



