THE DUCTLESS GLANDS 



terior part of the Cricothyroid muscles, the oesophagus (particularly on the left 

 side of the neck), the superior and inferior thyroid arteries, and the recurrent 

 laryngeal nerves. 



The deep surface of each lobe is fixed by bands of fibrous tissue passing from 

 the capsule of the isthmus and lateral lobes to the sides of the cricoid cartilage 

 and the posterior fascia of the trachea. These bands are called the lateral or 



suspensory ligaments. Because of this fixation 

 to the larynx and trachea by the capsule and 

 by the lateral ligaments, the thyroid gland 

 moves with the trachea and ascends during 

 the act of swallowing. The recurrent larvn- 

 geal nerve on each side is- in nqntaotjyitli 

 the outer and posterior surface of the sus- 

 pensory ligament. 



The anterior border is thin, and inclines 

 obliquely from above downward and inward 

 toward the middle line of the neck, while the 

 posterior border is thick and overlaps the com- 

 mon carotid artery. 



The isthmus (isthmus glandulae thyroidea) 

 connects the lower two-thirds of the two lat- 

 eral lobes; it measures about half an inch in 

 breadth and the same in depth, and usually 

 covers the second and third rings of the trachea, 

 hut sometimes also the first and fourth rings. 

 Its situation and size present, however, many 

 variations, a point of importance in the oper- 

 ation of tracheotomy. In the middle line of 

 the neck it is covered by the skin and fascia, 

 and close to the middle line, on either side, by 

 the Sternohyoid muscle. Across its upper 

 border run branches of the superior thyroid 

 artery and vein; at its lower border is a 

 branch of the inferior thyroid veins. Some- 

 times the isthmus is altogether wanting. 



The third, pyramidal or middle lobe frequently 

 arises from the upper part of the isthmus, or 

 from the adjacent portion of either lobe, but 

 most commonly from the left lobe, and ascends in front of the thyroid cartilage 

 in the direction of the middle of the hyoid bone. It may reach the bone or 

 may not reach it. If it reaches the bone it is attached to it. If it does not 

 reach the bone, fibrous tissue, which often contains muscle, is prolonged from the 

 tip of the pyramid to the back of the bone or to the thyrohyoid membrane. The 

 pyramid is occasionally quite detached, or divided into two or more parts. 



A few muscle bands, derived from the Thyrohyoid muscles, are occasionally 

 found attached, above, to the body of the hyoid bone, and below to the isthmus 

 of the gland or its pyramidal process. These form a muscle, which was named 

 by Soemmerring the Levator glandulae thyreoideae. 



Accessory Thyroids (glandulae thyreoideae accessor iae). Frequently small 

 isolated masses of thyroid tissue exist. They are found particularly about the 

 lateral lobes of the thyroid gland in the sides of the neck or just above the hyoid 

 bone, and are called accessory thyroids. 



Structure of the Thyroid (Fig. 1195). The thyroid body is invested by a capsule of con- 

 nective tissue which projects into its substance as a framework and imperfectly divides it into 



FIG. 1194. The thyroid gland. (Spalteholz.) 



