STYLO-HYOIDEUS. GENIOHYOIDEUS. 185 



between the anterior portions of the two muscles. This fascia is 

 named the supra-hyoidean. 



delations. By its superficial surface with the platysma myoides, 

 the sterno-mastoid, the anterior fasciculus of the stylo-hyoid muscle, 

 the parotid gland, and submaxillary gland. By its deep surface with 

 the styloid muscles, the hyo-glossus, the mylo-hyoid muscle, the ex- 

 ternal carotid artery, the lingual and the facial arteries, the in- 

 ternal carotid artery, the jugular vein, and the hypoglossal nerve. 

 The digastric muscle forms the two inferior boundaries of the sub- 

 maxillary triangle, the superior boundary being the side of the body of 

 the lower jaw. In the posterior half of the submaxillary triangle are 

 situated the submaxillary gland and the facial artery. 



The STYLO-HYOIDEUS is a small and slender muscle situated in 

 immediate relation with the posterior belly of the digastricus muscle, 

 being pierced by its tendon. It arises from the middle of the styloid 

 process, and is inserted into the body of the os hyoides near the 

 middle line. 



Relations. By its superficial surface with the posterior belly of the 

 digastricus, the parotid gland and sub-maxillary gland ; its deep re- 

 lations are similar to those of the posterior belly of the digastricus. 



The digastricus and stylo -hyoideus must be removed from their con- 

 nection with the lower jaw and os hyoides, and turned aside in order 

 to see the next muscle. 



The MYLO-HYOIDEUS (pvXv, mola, i. e. attached to the molar ridge 

 of the lower jaw) is a broad triangular plane of muscular fibres, form- 

 ing, with its fellow of the opposite side, the inferior wall or floor of the 

 mouth. It arises from the molar ridge on the lower jaw, and proceeds 

 obliquely inwards to be inserted into the raphe of the two muscles and 

 into the body of the os hyoides ; the raphe is sometimes deficient at its 

 anterior part. 



Relations. By its superficial or inferior surface, with the platysma 

 myoides, the digastricus, the supra-hyoidean fascia, the submaxillary 

 gland and the submental artery. By its deep or superior surface, with 

 the genio-hyoideus, the genio-hyo-glossus, the hyo-glossus, the stylo- 

 glossus, the gustatory nerve, the hypoglossal nerve, Wharton's duct, 

 the sublingual gland, and the mucous membrane of the floor of the 

 mouth. 



After the mylo-hyoideus has been examined, it should be cut away 

 from its origin and insertion, and completely removed. The view of 

 the next muscles would also be greatly improved by dividing the 

 lower jaw on the near side of the symphysis, and drawing it outwards, 

 or by removing it altogether if the ramus have been already cut across 

 in dissecting the internal pterygoid muscle. The tongue may then be 

 drawn out of the mouth by means of a hook. 



The GENIO-HYOIDEUS (ymav, the chin) arises from a small tubercle 

 upon the inner side of the symphysis of the lower jaw, and is inserted 

 into the upper part of the body of the os hyoides. It is a short and 

 slender muscle, very closely connected with the border of the following. 



