SUBMAXILLARY REGION 185 



both are bounded anteriorly and posteriorly by the anterior and 

 posterior bellies of the digastric muscle, the upper boundary of 

 the digastric triangle is the lower border of the mandible, whilst 

 the submaxillary region extends upwards to the level of the 

 mylo-hyoid ridge on the inner surface of the mandible. 



After the mandible has been turned upwards the dissector 

 should proceed, in the first place, to examine the relations of 

 the digastric and stylo -hyoid muscles, then the mylo-hyoid 

 muscle, and afterwards he must study the submaxillary and 

 sublingual glands and the deeper structures which are found in 

 the medial boundary of the submaxillary region. 



Musculus Digastricus. The digastric muscle limits the 

 submaxillary region inferiorly, and separates it from the 

 carotid and submental triangles (Figs. 67, 68). 



The anterior belly of the digastric springs from the inner 

 part of the lower border of the mandible, close to the 

 symphysis ; the posterior belly arises from the mastoid notch 

 of the temporal bone, on the medial side of the mastoid 

 process. The two bellies converge upon the upper border of 

 the hyoid bone, where they are united by an intermediate 

 tendon, which is attached to the hyoid bone, at the junction 

 of the body with the greater cornu, by a strong loop of fibrous 

 tissue developed from the deep cervical fascia. Posterior to 

 the loop, through which it plays, the intermediate tendon 

 passes through the cleft lower end of the stylo-hyoid muscle. 



Relations. The anterior belly is covered by the skin, 

 superficial fascia and the platysma, and the deep fascia. It 

 is overlapped by the anterior border of the submaxillary gland, 

 and its deep surface is in contact with the mylo-hyoid muscle. 

 Its anterior border is the posterior boundary of the submental 

 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. 



