418 THE MUSCLES AND FASCIA. 



gualis, passes round its margin and spreads out into a laye-r 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, and of vertical fibres, the Vertical lingualis. 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 constrictor of the pharynx. These transverse 

 extrinsic fibres, however, run in the opposite direction, passing inward, toward 

 the septum. Intersecting the transverse fibres are a large number of vertical fibres 

 derived partly from the Genio-hyo-glossus and partly from vertical 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 sub- 

 mucous 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 tongue, decussating Avith 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. At the sides of the under surface of 

 the tongue 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 Avhich joins in front 

 with the anterior fibres of the Inferior lingualis. The Inferior lingualis is a longi- 

 tudinal band, situated on the under surface of the tongue, lying in the interval 

 between the Stylo-glossus, in front of the Hyo-glossus, and the Genio-hyo-glossus, 

 and extending from the base to the apex of the organ. Posteriorly, some of the 

 fibres are lost in the base of the tongue, and others are occasionally attached to 

 the hyoid bone. It blends with the fibres of the Hyo-glossus, and is continued 

 forward as far as the apex of the tongue. It is in relation by its under surface 

 with the ranine artery. 



Surgical Anatomy. The fibrous septum which exists between the two halves of the 

 tongue is very complete, so that the anastomosis between the two lingual arteries is not very 

 free, a fact often illustrated by injecting one-half of the tongue with colored size, while the other 

 half is left uninjected or is injected with size of a different color. 



This is a point of considerable importance in connection with removal of one-half of the 

 tongue for cancer, an operation which is now frequently resorted to when the disease is strictly 

 confined to one side of the tongue. If the mucous membrane is divided longitudinally exactly 

 in the middle line, the tongue can be split into halves along the median raphe without any 

 appreciable haemorrhage, and the diseased half can then be removed. 



Actions. The movements of the tongue, although numerous and complicated, 

 may be understood by carefully considering the direction of the fibres of its 

 muscles. The G-enio-hyo-glossi muscles, by means of their posterior fibres, draw 

 the base of the tongue forward, so as to protrude the apex from the mouth. The 

 anterior fibres draw the tongue back into the mouth. The whole length of these 



