THE ANTERIOR PART OF THE NECK 223 



mastoid, and anteriorly by the median plane. Pass the index 

 finger from the chin to the sternum along the median line and 

 locate in sequence the body of the hyoid bone, the angular 

 anterior border of the thyreoid cartilage, the rounded arch of 

 the cricoid cartilage and the rings of the trachea. The latter 

 are partly masked by the isthmus of the thyreoid gland. 

 Place the thumb and the forefinger on the body of the hyoid 

 bone and carry them posteriorly, one on each side, along its 

 great cornua. Note that the posterior ends of the cornua lie 

 immediately in front of the anterior borders of the sterno- 

 mastoid muscles. Above the body of the hyoid bone lies the 

 submental triangle roofed in by the mylo-hyoid muscles, which 

 form the diaphragm of the mouth ; and above each great cornu 

 is the corresponding submaxillary region. Between the body 

 of the hyoid bone and the upper margin of the thyreoid 

 cartilage is the thyreo-hyoid space, bounded posteriorly by the 

 middle part of the thyreo-hyoid membrane, which lies anterior 

 to the upper part of the pharynx and the middle of the 

 epiglottis (Fig. 159). Trace the upper border of the thyreoid 

 cartilage posteriorly and note that it terminates on each 

 side in a pointed projection, the superior cornu, which lies 

 immediately in front of the anterior border of the sterno- 

 mastoid. Between the lower margin of the thyreoid cartilage 

 and the upper border of the cricoid cartilage lies the crico- 

 thyreoid ligament, forming part of the anterior wall of the 

 lower portion of the larynx. 



The dissectors should make themselves thoroughly familiar 

 with the landmarks mentioned above, both on their own necks 

 and on the necks of their friends, and they should note that 

 whilst in the dead subject there may be some difficulty in 

 palpating the isthmus of the thyreoid gland, as it crosses 

 anterior to the second, third, and fourth rings of the trachea, 

 they will have no difficulty in locating the small soft cushion- 

 like mass in the living subject. 



Dissection. The skin was cut along the lower border of the mandible 

 at the commencement of the dissection of the face ; now, make a median 

 incision through it from the chin to the sternum and turn the triangular 

 flap, thus marked out, posteriorly and laterally, to a short distance beyond 

 the anterior margin of the sterno-mastoid. When this is done the super- 

 ficial fascia covering the anterior triangle on each side will be exposed ; it 

 is thickest and most laden with fat in the submental region. In the upper 

 part of it lie the fibres of the platysma, running upwards and anteriorly 

 towards the mandible. The anterior fibres of the muscle gain attachment 

 to the anterior part of the lower border of the mandible, and some decussate 



