PARTS BENEATH THE MYLO-HYOID. 621 



At the hinder border of the hyo-glossus clean the lingual vessels, vessels, 

 lie stylo-hyoid ligament, and the glosso-pharyngeal nerve, all 

 passing beneath that muscle ; and at the anterior border find the 

 ssuing ranine artery, which, with the companion vein and lingual 

 lerve, is to be traced on the under surface of the tongue to 

 the tip. 



Adhering to the mucous membrane of the mouth is the sublingual and 

 ;land, and this is to be defined, together with the sublingual artery 

 which supplies it. 



Parts beneath the mylo-hyoid (fig. 224). The relative position of Parts be- 

 the objects covered by the mylo-hyoid is now apparent : Extending hyoid ; 

 rom the hyoid bone to the side of the tongue is the hyo-glossus 

 nuscle, the fibres of which are crossed superiorly by those of the above hyoid 

 ^tylo-glossus. On the hyo-glossus are placed, from below upwards, ne> 

 ;he hypo^lossal nerve, Wharton's duct, and the lingual nerve, the 

 [atler crossing the duct ; and near the anterior border of the muscle 

 :he two nerves are united by branches. Beneath the same muscle 

 ie, from below upwards, the lingual artery, the stylo-hyoid ligament, 

 ,nd the glosso-pharyngeal nerve. Above the hyo-glossus is the 

 mieous membrane of the mouth, with the sublingual gland attached 

 o it in front, and some fibres of the superior constrictor muscle 

 .'overing it behind near the jaw. 



Between the chin and the hyoid bone, close to the middle line, is in front of 

 situate the genio-hyoid muscle ; above this is a larger fan-shaped h>0 " glos 

 nuscle, the genio-glossus. Along the outer side of the last muscle 

 .ie the ranine vessels ; and a sublingual branch for the gland of the 

 same name springs from the lingual artery at the anterior border of 

 the hyo-glossus. On the under surface of the tongue, near the 

 margin, lies the lingual nerve ; and the hypoglossal nerve enters the 

 fibres of the genio-glossus. 



The HYO-GLOSSUS MUSCLE (fig. 223, i, p. 622, and fig. 222, c), is thin Hyo- 

 and somewhat square in shape. It arises from the lateral part of the gl h 

 oody, and from all the great cornu, of the hyoid bone. The fibres 

 ascend and enter the side of the tongue, extending from the base to 

 the tip, and they will afterwards be seen to mingle with those of the 

 palato- and stylo-glossus.* 



The parts lying on the outer surface of the hyo-glossus, as well as parts in 

 those passing beneath its anterior and posterior borders, have already contact ; 

 been enumerated ; and under the muscle there are also portions of 

 the geuio-glossus and middle constrictor. 



Action. This muscle depresses the tongue, drawing down the use. 

 sides and giving a rounded form to the dorsum ; and if the tongue 

 be protruded from the mouth, the fibres will draw it backwards into 

 that cavity. 



The STYLO-GLOSSUS (223, 2 ) is a slender muscle, which arises from Stylo- 



* A distinct muscular slip (chondro-glossus), aiising from the small cornu 

 of the hyoid hone, is sometimes regarded as a part of the hyo-glossus. For 

 farther details respecting the anatomy of this and the other lingual muscles, 

 reference should be made to the Section on the Tongue. 



