MUSCLES OF THE TONGUE. 



185 



The lower surface of the mylo-hyoid muscle is covered by the digastric muscle, the 

 submaxillary gland, and the submental vessels and nerve. The deep surface which 

 looks upwards and inwards to the mouth, is in contact with the genio-hyoideus and 

 part of the hyo-glossus and stylo- 

 glossus muscles, the ninth and gusta- 

 tory nerves, the sublingual gland, and pj a ^Q^ 

 the duct of the submaxillary gland 

 The posterior border alone is free and 

 unattached, and behind it the duct 

 of the submaxillary gland turns in 

 passing to the mouth. 



Fig 161. A, THE LOWER JAW AND 

 HYOID BONE, FROM BELOW, WITH 

 THE MYLO-HYOID MPSCLES AT- 

 TACHED. 



B, THE SAME, FROM BEHIND, WITH THE 



MYLO-HYOID AND GENIO-HYOID MUS- 

 CLES ATTACHED. | 



a, the symphysis ; b, the angle of 

 the lower jaw ; c, the lower border of 

 the body of the hyoid bone ; d, in B, 

 the inferior dental foramen and upper 

 end of the mylo-hyoid ridge : in A, 

 1, the left, 1', the right mylo-hyoid 

 muscle from below : in B, 1, the right, 

 1', the left mylo-hyoid muscle from 

 above ; 2, the right, 2', the left genio- 

 hyoid muscle from above; 3, the cut 

 ends of the attachment of the genio- 

 glossi muscles to the superior genial 

 spines. 



The genio-hyoid muscle, a narrow muscle resting on the mylo-hyoid, and 

 in contact with its fellow in the middle line, arises from the inferior of the 

 two genial tubercles behind the symphysis of the jaw, and is inserted into 

 the body of the hyoid bone. 



It is in contact above with the lower border of the genio-glossus muscle. 



ACTIONS. The genio-hyoid and mylo-hyoid muscles draw the hyoid bone upwards 

 and forwards, as happens in the first stage of deglutition. The stylo-hyoid muscle 

 draws it upwards and backwards, and comes into action in raising the pitch of the 

 voice. The anterior belly of the digastric muscle acts by itself like the genio- 

 hyoid, and the posterior half like the stylo-hyoid ; but when both bellies act 

 together they are capable of producing two movements, in one of which, when the 

 lower jaw is fixed, the hyoid bone is elevated, and in the other, when the hyoid 

 bone is held downwards by the depressing muscles, the digastric muscle opens the 

 mouth by depressing the lower jaw. 



B. MUSCLES OF THE TONGUE. 



The tongue is a muscular organ attached posteriorly to the hyoid bone, 

 and inferiorly to the lower jaw. It is composed partly of fibres peculiar to 

 itself the intrinsic muscles, which will be noticed in another place ; partly 

 of muscles arising from neighbouring parts ths extrinsic muscles about to 

 be described. 



The fjenio-glossus or genio-hyo-glossus muscle is fan-shaped, and is placed 

 vertically in contact with its fellow close to the mesial plane. It arises by 



