THE ANTERIOR PART OF THE NECK 127 



of the thyreoid body, secure the tributaries of the inferior 

 thyreoid veins at its lower border, and follow them downwards 

 to the upper aperture of the thorax ; then clearing away the 

 remains of the pretracheal fascia they should display the front 

 of the lower part of the cervical portion of the trachea upon 

 which the inferior thyreoid veins descend. At this stage a 

 small artery, the thyreoidea ima, may occasionally be found 

 ascending on the front of the trachea to the isthmus of the 

 thyreoid body. 



When the dissection of the lower part of the infra-hyoid area 

 is completed return to the upper part. Clean the anterior ends 

 of the crico-thyreoid muscles which spring from the cricoid 

 cartilage ; they run upwards and laterally, one on each side. 

 Between the crico-thyreoid muscles, on a deeper plane, secure 

 the crico-thyreoid arteries, which anastomose across the front 

 of the median crico-thyreoid ligament. Note that the median 

 crico-th)^reoid ligament is attached below to the upper border 

 of the cricoid cartilage, and above to the lower border of the 

 thyreoid cartilage ; then push the handle of the scalpel or a broad 

 probe backwards along the surface of the conus elasticus, which is 

 continuous with the median ligament, and note that it ascends 

 medial to the thyreoid cartilage. It becomes continuous above 

 (see Fig. 126), with the vocal ligament, but that fact cannot be 

 demonstrated at the present stage of the dissection. Next clean 

 the prominent anterior part of the thyreoid cartilage, which forms 

 the laryngeal prominence in the front of the neck. Lastly, 

 clean away the fascial tissue between the upper part of the 

 thyreoid cartilage and the body of the hyoid bone and display 

 the middle thyreo-hyoid ligament which extends from the 

 upper border of the thyreoid cartilage behind the body of the 

 hyoid bone to its upper border. As the fascia is removed from 

 the upper part of the median thyreo-hyoid ligament behind the 

 body of the hyoid bone a small bursal sac will be opened. It 

 facilitates the movement of the hyoid bone over the upper part 

 of the thyreoid cartilage during deglutition. When the dissec- 

 tion is completed revise the structures which have been exposed. 



The Middle Line of the Neck. In the supra-hyoid part 

 of the median portion of the neck lie the structures which 

 are concerned in the construction of the floor of the mouth. 

 The dissector will have noticed already that the fatty superficial 

 fascia was more fully developed there than elsewhere in the 

 neck, and that the anterior margins of the two platysma 

 muscles met and decussated in the median plane, for 10 or 

 1 2 mm. (about half an inch), below the chin. The anterior 

 attachments of the bellies of the two digastric muscles to the 

 mandible, one on each side of the symphysis, was noted. 

 Thence they descend towards the hyoid bone, and diverge 

 slightly from each other so as to leave between them a narrow 

 triangular space, called the submental triangle (Fig. 44). The 

 floor of the space is formed by the anterior portions of the 



