THE NECK 167 



lobes. The position and relations of the isthmus are referred 

 to on p. 163. Each lateral lobe is conical in shape ; the broad 

 base extends downwards as far as the sixth ring of the trachea, 

 and the apex passes upwards on to the lamina of the thyreoid 

 cartilage. The medial surface of the lateral lobe is closely 

 applied to the trachea and larynx, in front, and to the cesophagus 

 and pharynx, behind. Postero-laterally the gland is in contact 

 with the carotid sheath, while its antero-lateral surface lies 

 under cover of the depressor muscles of the hyoid bone (Fig. 36). 

 Sometimes an additional lobe the pyramidal lobe is present. 

 It ascends from the upper border of the isthmus on one or other 

 side of the median plane, and it may be attached to the hyoid 

 bone by a fibre-muscular slip, termed the levator glandulse 

 thyreoideae. 



The pretracheal fascia invests the gland with & fibrous sheath, 

 which is thickest on its deep and postero-lateral aspects, and is 

 very adherent to the trachea behind the isthmus. The gland 

 can easily be separated from its sheath, save on the posterior 

 aspect of the isthmus where the two are intimately connected. 

 In addition to its loose fascial sheath, the gland is provided 

 with a complete fibrous capsule, which envelops it closely, and 

 sends in numerous fibrous septa to separate the lobules and acini 

 from one another. The numerous blood-vessels of the gland 

 run in the fibrous septa, and are brought into close contact with 

 the outer aspects of the acini. 



The blood-supply of the thyreoid gland is derived from the 

 superior and inferior thyreoid arteries (pp. 121, 143). The former 

 is mainly distributed to the medial surface of the upper pole of 

 the lateral lobe and to the isthmus ; the latter supplies the 

 lower pole and lateral surface. Both arteries pierce the fascial 

 sheath posteriorly, and are then associated with the parathyreoid 

 glands (p. 169). 



In the operation of Thyreoidectomy it is advantageous 

 to have the patient's head, neck, and thorax on a slight upward 

 incline in order to diminish the haemorrhage. Kocher's collar 

 incision or the angular incision may be employed, and both give 

 good access to the gland. The angular incision begins on the 

 posterior border of the sterno-mastoid at the level of the hyoid 

 bone, passes downwards and medially to the cricoid cartilage, 

 and is then carried vertically downwards in the median line to 

 the jugular (supra-sternal) notch. In the upper part of the wound 

 the incision is deepened through the superficial fascia and the 



116 



