SUBMAXILLARY REGION 281 



triangle, and its posterior border is the anterior boundary of 

 the digastric triangle. 



The' relations of the posterior belly are more numerous 

 and important. Posteriorly, it is covered by the mastoid 

 process and the attachments of the sterno-mastoid and 

 splenius capitis muscles. Between the mastoid process and 

 the angle of the mandible it forms part of the postero-medial 

 boundary of the parotid space and is covered by the parotid 

 gland ; next it is covered by the angle of the mandible and 

 the insertion of the internal pterygoid muscle. As it lies in 

 the anterior triangle it is covered by the skin, the superficial 

 fascia and platysma, and the deep fascia; it is crossed by 

 the anterior facial vein, and is overlapped by the posterior 

 part of the submaxillary gland. 



It is superficial to the internal jugular vein, the internal 

 and the external carotid arteries, the external maxillary artery, 

 the middle constrictor of the pharynx, and the lower and 

 posterior part of the hyoglossus muscle. The accessory 

 nerve passes posteriorly and down wards ^et ween it and the 

 internal jugular vein, and the occipital artery passes upwards 

 and posteriorly 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 anteriorly and downwards 

 between it and the internal carotid. The posterior auricular 

 artery runs upwards and posteriorly 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. ^ 



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

 anterior belly by the mylo-hyoid branch of the inferior alveolar 

 nerve. 



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 great 

 cornu with the body. Its main relations are practically the 

 same as those of the posterior belly of the digastric, but it is 



