284 HEAD AND NECK 



The medial surface is in relation with the mylo-hyoid and 

 hyoglossus, the lingual nerve and the submaxillary ganglion, 

 and the hypoglossal nerve. It overlaps the stylo-hyoid 

 muscle, both bellies of the digastric, and the great cornu of 

 the hyoid bone ; and the deep part of the gland and the duct 

 both spring from this surface before they pass anteriorly 

 between the mylo-hyoid and the hyoglossus muscles. 



The nerve supply of the gland is derived from the lingual 

 nerve, the submaxillary ganglion, the sympathetic plexus on 

 the external maxillary artery ; and its vascular supply consists 

 of small submaxillary branches from the external maxillary 

 artery. 



The relations of the deep part of the gland and the duct 

 will be investigated after the mylo-hyoid has been reflected. 



Dissection. Displace the superficial part of the gland and the submental 

 branch of the external maxillary artery posteriorly ; cut the mylo-hyoid 

 vessels and nerve, and turn the anterior belly of the digastric downwards ; 

 then clean the mylo-hyoid muscle and examine its attachments. 



Musculus Mylohyoideus. This is a thin sheet of 

 muscular fibres, which arises from the mylo-hyoid ridge 

 upon the inner surface of the body of the mandible, by 

 an origin which extends from the last molar tooth to the 

 symphysis. Its fibres are directed downwards, medially, 

 and anteriorly, and present two different modes of insertion. 

 The posterior fibres are inserted into the body of the hyoid 

 bone ; these, however, form a comparatively small part of 

 the muscle. The greater number of the fibres are inserted 

 into a median raphe, which extends between the symphysis 

 of the lower jaw and the body of the hyoid bone. The 

 two mylo-hyoid muscles, therefore, stretch across from one 

 side of the body of the mandible to the other, in front of the 

 hyoid bone, and constitute a floor for the anterior part of the 

 mouth. This floor is frequently termed the diaphragma oris. 

 The mylo-hyoid muscle is supplied by the mylo-hyoid branch 

 of the inferior alveolar nerve. 



Dissection. Cut the mylo-hyoid muscle a little below its origin from the 

 mylo-hyoid ridge and turn it downwards and anteriorly. Whilst doing 

 this be careful not to injure the mucous membrane of the mouth which 

 lies in contact with it above. 



Parts exposed by the Reflection of the Mylo-hyoid (Fig. 

 115). The side of the tongue is now brought into view, 

 with a number of structures in connection with it. First 



