326 THE MUSCLES AND FASCIA. 



section may then be commenced from the dorsum (Fig. 206). Immediately 

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

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

 removing this, with the mucous membrane, the first stratum of muscular fibres is 

 exposed. This belongs to the group of intrinsic muscles, and has been named the 

 Superior lingualis (m. longitudinalis superior}. It consists of a thin layer of 

 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- 

 gualis, passes round its margin and spreads out into a layer on the dorsum, which 

 occupies the middle third of the organ, and runs almost transversely inward to the 

 septum. It is reinforced by some fibres from the Palato-glossus ; other fibres of this 

 muscle pass more deeply and intermingle with the next layer. The posterior part 

 of the second layer of the muscular fibres of the tongue is derived from those 

 fibres of the Hyo-glossus which arise from the lesser cornu of the hyoid bone, and 

 are here described as a separate muscle the Chondro-glossus. The fibres of this 

 muscle are arranged in a fan-shaped manner, and spread out over the posterior 

 third of the tongue. Beneath this layer is the great mass of the intrinsic muscles 

 of the tongue, intersected at right angles by the terminal fibres of one of the 

 extrinsic muscles the Genio-hyo-glossus. This portion of the tongue is paler 

 in color and softer in texture than that already described, and is sometimes 

 designated the medullary portion in contradistinction to the firmer superficial part, 

 which is termed the cortical portion. It consists largely of transverse fibres, the 

 Transverse lingualis (m. transversus linguae), and of vertical fibres, the Vertical 

 lingualis (m. verticulis lingua;}. The Transverse lingualis forms the largest portion 

 of the third layer of muscular fibres of the tongue. The fibres arise from the 

 median septum, and pass outward to be inserted into the submucous fibrous layer 

 at the sides of the tongue. Intermingled with these transverse intrinsic fibres are 

 transverse extrinsic fibres derived from the Palato-glossus and the Superior con- 

 strictor of the pharynx. These transverse extrinsic fibres, however, run in the 

 opposite direction, passing inward toAvard the septum. Intersecting the transverse 

 fibres are a large number of vertical fibres derived partly from the Genio-hyo- 

 glossus and partly from intrinsic fibres, the Vertical lingualis. The fibres derived 

 from the Genio-hyo-glossus enter the under surface of the tongue on each side of 

 the median septum from base to apex. They ascend in a radiating manner to the 

 dorsum, being inserted into the submucous fibrous layer covering the tongue on 

 each side of the middle line. The Vertical lingualis is found only at the borders 

 of the fore part of the tongue, external to the fibres of the Genio-hyo-glossus. 

 Its fibres extend from the upper to the under surface of the organ, decussating 

 with the fibres of the other muscles, and especially with the Transverse lingualis. 

 The fourth layer of muscular fibres of the tongue consists partly of extrinsic fibres 

 derived from the Stylo-glossus, and partly of intrinsic fibres, the Inferior lingualis 

 (m. longitudinalis inferior). At the sides of the under surface of the organ are 

 some fibres derived from the Stylo-glossus, which, as it runs forward at the side of 

 the tongue, gives off fibres which, passing forward and inward between the fibres 

 of the Hyo-glossus, form an inferior oblique stratum which joins in front with the 



