2 30 HEAD AND NECK 



along the anterior surface of the trachea, and it blends below with the 

 fibrous pericardium. 



Remove the pretracheal fascia from the region of the intermuscular 

 interval, first above and then below the isthmus of the thyreoid gland. As 

 the fascia is dissected away the following structures will be displayed. 

 Immediately below the thyreoid cartilage is the crico-thyreoid ligament, 

 overlapped on each side by the anterior part of the crico-thyreoid muscle. 

 Crossing anterior to the ligament, transversely, is the anastomosis 

 between the crico-thyreoid branches of the superior thyreoid arteries. 

 It lies nearer the lower than the upper border of the ligament. Below 

 the crico-thyreoid ligament is the convex anterior part of the cricoid 

 cartilage ; then follows the crico-tracheal ligament, uniting the cricoid 

 cartilage to the first ring of the trachea. The isthmus of the thyreoid 

 gland lies at a lower level opposite the second, third, and fourth rings of 

 the trachea. Along its upper border is the anastomosis between the 

 medial terminal branches of the superior thyreoid arteries, and below it 

 are the lower cervical tracheal rings. 



The superficial layers of the deep fascia must now be removed from the 

 whole area of each anterior triangle, and for this purpose and for the 

 satisfactory dissection of the contents of the triangles, it is necessary that 

 the head be turned well over to the opposite side ; therefore the dissectors 

 must arrange to work alternately. 



Commence with the digastric triangle. Its boundaries are 

 the lower border of the mandible and the two bellies of the 

 digastric muscle. 



Its contents are: (i) the lower part of the submaxillary 

 gland; (2) the submaxillary lymph glands; (3) part of the 

 external maxillary artery ; (4) part of the anterior facial vein ; 

 (5) the mylo-hyoid nerve; (6) the mylo-hyoid artery; (7) a 

 small part of the hypoglossal nerve ; (8) a small part of the 

 lingual vein. 



Dissection. Remove the deep fascia which was previously turned aside 



y lymph glands. Most of 

 lie immediately below the mandible in the angle between it and the sub- 



(p. 225) and clean the submaxillary lymph glands. Most of these glands 



maxillary gland, but some may be found on the superficial surface of the 

 gland. Turn the gland upwards and fix it with hooks ; then secure the 

 mylo-hyoid nerve and artery as they enter the posterior border of the 

 anterior belly of the digastric about the middle of its length. Define the 

 band of fascia which surrounds the intermediate tendon of the digastric and 

 binds it to the great cornu of the hyoid bone. Note that the tendon is em- 

 braced by the cleft lower end of the stylo-hyoid muscle. Clean the posterior 

 belly of the digastric and the stylo-hyoid muscle which descends along its 

 anterior border. Note that the posterior belly of the digastric and the 

 stylo-hyoid disappear, postero-superiorly, under cover of the angle of the 

 mandible. Clean the anterior belly of the digastric, and then examine 

 the floor or medial boundary of the triangle. Immediately behind the 

 anterior belly of the digastric it is formed by the posterior fibres of the 

 mylo-hyoid muscle ; and more posteriorly and on a deeper plane it is 

 formed by the hyoglossus. 



Clean the portion of the mylo-hyoid which is exposed and, at its 

 posterior border, immediately above the great cornu of the hyoid bone, 



