226 HEAD AND NECK 



and lower part of the submaxillary gland usually overlaps the 

 stylo-hyoid and the posterior belly of the digastric muscles, 

 and not infrequently it overlaps the great cornu of the hyoid 

 bone also. Its anterior border may overlap the anterior 

 belly of the digastric. Raise the lower border of the gland 

 and expose another layer of deep fascia covering the muscles 

 which lie deep to it. Place the handle of the knife on this 

 fascia and push it gently upwards. Note that it passes 

 upwards to the level of the mylo-hyoid line on the inner surface 

 of the mandible, to which the mylo-hyoid muscle is attached. 

 The fascial sheath in which the submaxillary gland is enclosed 

 consists, therefore, of a superficial layer of deep fascia which 

 extends from the great cornu of the hyoid bone to the lower 

 border of the mandible, and a deeper layer which passes from 

 the great cornu of the hyoid to the mylo-hyoid line of the 

 mandible. The two layers blend in front of the anterior 

 belly of the digastric, and posteriorly they unite, behind the 

 posterior belly of the digastric, with the connective tissue in 

 which the carotid vessels are embedded. 



Dissection. Remove the deep fascia in the region of the anterior 

 triangle and expose the divisions and the contents of the triangle. 



The Divisions of the Anterior Triangle. After the deep 

 fascia is removed, the dissector will recognise that each 

 anterior triangle may be divided into three subsidiary areas 

 which are called the digastric, the carotid, and the muscular 

 triangles, by means of the two bellies of the digastric muscle 

 and the anterior belly of the omo-hyoid muscle. 



The digastric triangle is bounded by the two bellies of the 

 digastric muscle and the lower border of the mandible. 



The boundaries of the carotid triangle are, above and in 

 front, the posterior belly of the digastric ; below and in front, 

 the anterior belly of the omo-hyoid ; and, behind, the anterior 

 border of the sterno-mastoid. 



The muscular triangle is bounded, above and behind, by 

 the anterior belly of the omo-hyoid ; below and behind, 

 by the anterior border of the sterno-mastoid ; and in front, 

 by the middle line of the neck. 



An additional triangle common to the two sides lies between the hyoid 

 bone below, the two anterior bellies of the digastrics laterally, and the 

 mandible above. This is called the submental triangle, 



The Middle Line of the Neck. Before commencing the 



