284 



MUSCLES OF THE HEAD AND NECK. 



Vaj-irties. — This muscle may be inseparably united with, and even upon't'ono 

 side replaced by the anterior belly of the digastric. It frequently receives an 

 accessory slip from one of the other hyoid muscles, as the stemo-hyoid, omo- 

 hyoid, or Btylo-hyoid. 



The genio-liyoid is a narrow muscle arising from the inferior of the 

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

 the anterior surface of the body of the hyoid bone. 



JRelathn.t. — It is in contact above with the lower border of the genio-g-lossus 

 muscle, and below with the mylo-hyoid and with its fellow in the middle line. 



Nerves. — Tlie muscles of this group receive their motor nerves from various 

 sources, viz., the anterior belly of the digastric and the mylo-hyoid from 

 the mylo-hyoid branch of the inferior maxillary division of the fifth nei-ve, an,I 

 the posterior belly of the digastric and the stylo-hyoid from the facial nerve near 

 the place of its exit from the stylo-mastoid foramen, Tlie genio-hyoid receives 

 its motor nerve from the hypoglossal. 



Actions. — The genio-hyoid and mylo-hyoid muscles di'aw the hyoid bone 

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

 hyoid muscles di-aw it upwards and backwards, and come into action in raising 

 the pitch of the voice. The anterior beUy of the digastric muscle acts by itself 

 like the genio-hyoid and the jjosterior half like the stylo-hyoid ; but when both 



bellies act together they are 

 Fig. 210. 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 

 hj'oid bone is held do-mi wards 

 by the depressing muscles, 

 the lower jaw is depressed. 



Fig. 210. — Muscles op ths 

 Tongue, Pharynx, &c., ok 

 the left side. (a. t.) -^ 



a, external pterygoid pro- 

 cess ; h, styloid process ; c, 

 section of the symphysis of the 

 lower jaw ; d, front of the 

 body of the hyoid bone ; c, 

 thyroid cartilage ; /, cricoid 

 cartilage ; between d and c, 

 the tliyro-hyoid membrane and 

 ligament ; g, isthmus of the 

 thyroid gland ; 1, stylo-glossus 

 muscle ; 2, stylo-hyoid ; 3, 

 stylo-pharyngeus ; 4, cut edge 

 of the mylo-hyoid ; 5, genio- 

 hyoid ; 6, genio-hyo-glossus ; 7, 

 Lyo-glogsus ; 8, linguaUs in- 

 ferior ; 9, part of the superior 

 constrictor of the phaiynx ; 10, 

 back part of tlie middle con- 

 strictor ; 11, inferior consti'ictor; 

 12, upper part of the o?sopha- 

 gus ; 13, crico-thjToid muscle. 



MUSCLES OP 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 



