THE TONGUE. 



1129 



run towards the tip ; the arteries, however, are deeply placed in the substance of the tongue, 

 at a distance of 3 to 6 mm. from the inferior surface. The plicae, which are more distinct at birth 

 and in the foetus, are said to correspond to the under tongue found in the lemurs. 



The root of the tongue is the portion of the inferior aspect which is con- 

 nected by muscles and mucous membrane to the mandible and hyoid bone. It is 

 of very considerable extent, and is, with the base, the most fixed part of the 

 organ. It is also the situation at which the vessels, nerves, and the extrinsic 

 muscles enter. 



Structure of the Tongue. The tongue is composed chiefly of striped muscular 

 tissue, with a considerable admixture of fine fat. A median septum of connective 

 tissue occupies the central part of the organ. In addition, there are vessels, nerves, 

 glands, and lymph tissue, the whole being covered over by mucous membrane, except at 

 the root (Fig. 893). 



The muscular tissue is derived partly from the terminations of the extrinsic muscles 

 namely, the hyoglossus, styloglossus, genioglossus, glossopalatinus, and chondroglossus ; 

 and also largely from the intrinsic muscles namely, the longitudinalis superior, 

 the longitudinales inferiores, the transversus linguae, and the verticalis linguse. These are 

 so arranged that they form a cortical portion, made up chiefly of longitudinal fibres 

 derived, above, from the longitudinalis superior and the hyoglossus, at the sides, from 



Transversus M. verticalis 

 linguae lingupe 



M. longitudinalis 

 superior 



Nodules of 

 lymph tissue 



>funda artery 



Mucous glands 



Transversus linguae 

 liongitiidinalis inferior 



5. A, TRANSVERSE, AND B, LONGITUDINAL VERTICAL SECTION THROUGH THE TONGUE (Krause) ; 

 C, A LYMPH FOLLICLE FROM POSTERIOR PART OF THE TONGUE. (Macalister, slightly modified.) 



the styloglossus, and, below, from the longitudinales inferiores. This cortex surrounds a 

 central or medullary portion, divided into two halves by the median septum, and formed 

 in great part by the transverse and vertical fibres, and also by the fibres of the genio- 

 glossi ascending to the dorsum. The muscular fibres derived from these various sources 

 end by being inserted into the deep surface of the mucous membrane. 



The detailed description of the extrinsic and intrinsic muscles will be found on 

 page 462. 



The septum is a median fibrous partition found in the medullary portion only, and 

 easily exposed by separating the two genioglossi on the inferior surface of the tongue. 

 Anteriorly it usually extends to the apex ; whilst posteriorly it grows gradually narrower, 

 and expanding transversely at the same time, it passes into a broad sheet (the hyoglossal 

 membrane) which is united to the upper border of the hyoid bone, and gives attachment 

 to the posterior fibres of the genioglossus. From the sides of the septum the fibres of the 

 transverse muscle of the tongue arise. 



The mucous membrane on the anterior two-thirds of the dorsum, and on the free 

 margins, is firm and closely adherent to the underlying muscular substance, the fibres 

 )f which are inserted into it. On the posterior third of the dorsum, and on the inferior 

 surface, it is neither so firm nor so closely united to the muscular substance, from which 

 t is separated in both of these situations by a layer of submucous tissue. 



