MUSCLES OF THE TRUNK. 2S1 



turned down by isolating the mylo-hyniilcus from tlic mucous membrane. 5. Carefully remove 

 the tongue by separating its extrinsic muscles from the genio-hyoideus, the anterior appendix 

 of tiif liyoid bone, the transverse muscle, and tlie small hyoideus. 



The dissection having been performed in this manner, the large hyoideal branch may be 

 separated from the small, by sawing through the head longitudinally, leaving the symphysis 

 menti intact, and turning down the corresponding half to the side already dissected, as well as 

 the great hyoid branch, the pharynx, larynx, and soft palate. 



1. Mylo-hyoideus. 



Form — Situation — Structure. — A membranous muscle situated in the inter- 

 maxillary space, flattened from side to side, elongated in the direction of the 

 head, thinner and narrower below than above, and formed entirely of fleshy fibres 

 which extend transversely from its anterior to its posterior border. Inferiorly, 

 it is composed of a small fasciculus, which is distinguished from the principal 



Fig. 171. 



HTOrOEAL AND PHARTNGEAL REGIONS. 



1, Neck of inferior maxilla ; 2, hard palate ; .3, molar teeth : 4, buccal membrane ; 5, submaxillary 

 glands; 6, soft palate; 7, ten'ion of hyoideus magniis throu2;h which the tendon, 8, of the 

 digastricns passes; 9, lower portion of digastricus ; 10, stylo-hyoideus ; 11, buccal nerve; 12, 

 zygomatic arch; 13, orbital branch of fifth pair of nerves; 14, articular process of temporal 

 bone; 15, right cornu of hyoid bone; 16. hyo-glossus longus, or Kerato-glossus ; 17, lingual 

 nerve; 18, 18, tongue; 19, angle of left branch of inferior maxilla; 20, submaxillary gland, 

 left side ; 21, subscapulo-hyoideus ; 22, great hypoglossal nerve ; 23, hyo-thyroideus ; 24, sterno- 

 hyoideus; 25, sterno-thyroidous; 26, subscapulo hyoideus; 27, thyroid gland; 28, external 

 carotid artery ; 29, pneuraogastric nerve ; 30, stylo-hyoideus ; 31. genio-hyoideus. 



portion by the slightly different direction of its fibres, and which covers in part 

 the external surface of the muscle. 



Attachments. — It originates from the mylo-hyoid line by the anterior 

 extremities of its fibres. Its movable insertion takes place on the inferior face 

 of the hyoid body, on its anterior appendix, and on a fibrous raph^ which extends 

 from the free extremity of this appendix to near the genial surface, and which 

 unites, on the median line, the two mylo-hyoidean muscles. 



Relations. — By its external face, with the inferior maxilla, the digastricus, 

 and the submaxillaiy lymphatic glands. By its internal face, with the sublingual 

 gland, the Whartonian duct, the hypoglossal and lingual nerves, the genio-glossus, 

 hyo-glossus longus and brevis, and genio-hyoideus. Its superior border responds 

 to the internal pterygoid. 



Action. — In uniting on the median Line with that of the opposite side, this 



