200 THE ANATOMY OF THE HOK.SE. 



Action. — To aid in retracting the tongue. 



The Genio-glossus, or Genio-hyo-glossus (Plates 31 and 32). This 

 muscle is ftm-shaped. Its origin is from a depression on the inner 

 surface of the horizontal ramus of the lower jaw, near the symphysis. 

 From this point, and from a tendon at the posterior edge of the muscle, 

 its fibres radiate into the tip, centre, and base of the tongue, beneath 

 those of the stylo-glossus and great hyo-glossus muscles. 



Action. — The upper fibres protrude the tongue by pulling downwards 

 its base, the lower fibres retract the free portion of the tongiie, and 

 the intermediate fibres (or the entire muscle) depress the tongue as a 

 whole towards the floor of the mouth. 



If the dissector will raise the posterior tendinous edge of the muscle, 

 he will find that he has now reached the middle plane of the tongue, 

 which is here occupied by a quantity of connective-tissue and fat 

 between the right and left genio-glossus nmscles. 



The Genio-hyoideus (Plates 31 and 32). This is a muscle of the 

 hyoid bone, rather than of the tongue. It is elongated and fusiform in 

 shape, and is placed beneath the tongue, near the middle line. It arises 

 from the inner surface of the horizontal ramus, close to the symphj'sis; 

 and passing upwards along the inner edge of the mylo-hyoid, it 

 becomes inserted into the glossal or spur process of the hyoid bone. 



Action. — To pull forwards the hj-oid bone. 



The Lingual Artery (Plate 32). This is a large branch of the sub- 

 maxillary artery, and has already been seen at its origin. It passes 

 under cover of the great hyo-glossus, crossing the small cornu of the 

 hyoid bone. In passing to the root of the tongue, it crosses obliquely 

 forwards and downwards beneath the middle hyo-glossiis and the palato- 

 glossus. In the body of the tongue it lies beneath tlie great hyo-glossus, 

 and in the free portion of the tongue it is internal to the stylo-glossus. 

 In its course it becomes reduced in size by detaching lateral branches, 

 and it terminates at the tip of the tongue by turning inwards and 

 anastomosing on the middle line with the vessel of the opposite side. 

 Like the lingual nerve, the artery is flexuous in the inferior part t)f the 

 tongue, that it may be adapted, without stretching, to the varying 

 length of the organ. 



The Glosso-pharyngeal (9th) Nerve (Plate 32). The lingual 

 continuation of this nerve will be found crossing the inner side of the 

 articulation between the great and small cornua of the hyoid bone to 

 reach the base of the tongue. Here it divides into branches for the 

 mucous membrane on the superior third of the tongue. 



THE hard palate (fIG. 21). 



The surface of the hard palate is covered by a dense mucous 

 membrane having a stratified squamous epithelium. It is traversed in 



