1 90 HEAD AND NECK 



before they pass forwards between the mylo-hyoid and the 

 hyoglossus muscles (Fig. 71). 



The nerve supply of the gland is derived from the lingual 

 nerve, the submaxillary ganglion, and the sympathetic plexus 

 on the external maxillary artery ; its vascular supply consists 

 of small glandular 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 backwards ; 

 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. The mylo-hyoid muscle is a 

 thin sheet of muscular fibres, which arises from the mylo- 

 hyoid line upon the medial 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 forwards, and present two different modes of 

 insertion. The posterior fibres are inserted into the body of 

 the hyoid bone ; they, however, form a comparatively small 

 part of the muscle. Most of the fibres are inserted into a 

 median raphe which extends between the symphysis of 

 the mandible 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 which is frequently termed the diaphragma oris. The 

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

 the inferior alveolar nerve. It elevates the hyoid bone, the 

 tongue and the floor of the mouth in the movement of 

 swallowing. 



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

 origin from the mylo-hyoid ridge and turn it downwards and 

 forwards. Be careful not to injure the mucous membrane of 

 the mouth, which lies in contact with the upper surface of the 

 muscle near its origin. 



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

 70). Part of the tongue, and a number of structures 

 associated with it are now brought into view. First, note 

 the mucous membrane stretching from the tongue to the 



