SUBMAXILLARY REGION 187 



the middle constrictor of the pharynx, and the lower and 

 posterior part of the hyoglossus muscle. The accessory 

 nerve passes backwards and downwards between it and the 

 internal jugular vein, and the occipital artery passes upwards 

 and backwards under cover of its lower border, superficial 

 to the accessory nerve. The hypoglossal nerve descends 

 vertically on its deep surface in the angle between the 

 internal jugular vein and the internal carotid artery, and 

 the glosso-pharyngeal nerve passes forwards and downwards 

 between it and the internal carotid. The posterior auricular 

 artery runs upwards and backwards along the posterior part 

 of its upper border under cover of the postero-medial surface 

 of the parotid, and the stylo-hyoid muscle descends along the 

 same border (Fig. 68). 



The posterior belly is supplied by the facial nerve, and the 

 anterior belly is supplied by the mylo-hyoid branch of the 

 inferior alveolar nerve. 



If the digastric acts from its posterior attachment it 

 depresses the mandible. If the mandible is fixed and the 

 diagastric acts from its anterior attachment it helps to pull 

 the head backwards. If both the bellies act simultaneously 

 the hyoid bone is raised. 



Musculus Stylohyoideus. The stylo-hyoid muscle is a 

 small muscular bundle which springs from the posterior 

 border and lateral surface of the middle third of the styloid 

 process and descends along the upper border of the posterior 

 belly of the digastric. It divides below into two slips 

 which embrace the intermediate tendon of the digastric 

 and are then inserted into the hyoid bone, at the junction 

 of the greater cornu with the body. Its main relations 

 are practically the same as those of the posterior belly of the 

 digastric, but it is not under cover of the mastoid process, 

 the sterno-mastoid, and the spienius muscles. It is supplied 

 by the facial nerve. It raises the hyoid bone and draws it 

 backwards. 



Dissection. Turn the anterior part of the submaxillary 

 gland backwards, and clean the posterior part of the mylo-hyoid 

 muscle, which lies deep to it. Note that a process, the deep part 

 of the gland, springs from the medial surface of the superficial 

 part and passes forwards, deep to the mylo-hyoid. Dissect the 

 external maxillary artery out of the deep sulcus in the posterior 

 part of the gland, without injuring its submental branch, which 

 runs forwards, along the lower border of the mandible ; then 



