58l 



DISSECTIOK OF THE XK(.'K. 



relations : 



Thyro- 

 hyoid 



muscle 



Thyroid 

 body 



consists of 

 two lobes 

 and a cross 

 piece. 



llelatious 

 and 



extent of 

 lobes. 



Middle lobe 

 or pyramid. 



Accessory 

 glands. 



sterno-hyoid, and is inserted into the oblique line on the side of the 

 thyroid cartilage, where it meets the thyro-hyoid muscle. 



The inner border touches its fellow below, while the outer 

 reaches over the carotid artery. The superficial surface is for the 

 most part covered by the preceding hyoid muscles ; and the 

 deep surface is in contact with the lower part of the common 

 carotid artery, the trachea, the larynx, and the thyroid body. A 

 transverse tendinous line frequently crosses the muscle near the 

 sternum. 



Action. Its chief use is to draw downwards the larynx after 

 deglutition, but in conjunction with the following muscle it can 

 also act on the hyoid bone. 



Like the sterno-hyoid it participates in the movement of the 

 chest in laborious breathing. 



The THYRO-HYOID MUSCLE (fig. 211, 4 ) forms a continuation of 

 the sterno-thyroid. Arising from the oblique line of the thyroid 

 cartilage, the fibres ascend to the anterior half of the great cornu, 

 and the outer part of the body of the hyoid bone. 



On the muscle lie the omo-hyoid and the sterno-hyoid ; and 

 beneath it are the superior laryngeal nerve and vessels. 



Action. It draws up the larynx towards the hyoid bone, as in 

 swallowing. The sterno-thyroid and thyro-hyoid together fix the 

 thyroid cartilage for the action of the intrinsic muscles of the 

 larynx. 



Dissection. The sterno-hyoid and sterno-thyroid muscles should 

 now be raised and the thyroid gland cleaned as it overlies the larynx 

 and trachea. The muscles should not be divided but should be 

 rendered slack for the purpose required by bending the neck for- 

 ward. Care should be taken not to injure the vessels of the gland, 

 and the inferior thyroid vein should be cleaned as it runs down the 

 front of the trachea. 



The THYROID BODY (fig. 212 and fig. 213, 13 , p. 589) is a soft 

 reddish mass, which embraces the upper part of the trachea. It 

 consists of two lateral lobes, united by a narrow piece across the 

 front of the windpipe. The connecting piece, from a quarter to 

 three-quarters of an inch in depth, is named the isthmus, and is 

 placed over the second, third, and fourth rings of the trachea. 



Each lobe is somewhat conical in shape, with the smaller end 

 upwards, and is about two inches in length. It is interposed 

 between the windpipe with the larynx and the sheath of the common 

 carotid artery, and is covered by the sterno-thyroid, sterno-hyoid, 

 and omo-hyoid muscles. The extent of the lobe varies ; but usually 

 it reaches as high as the middle of the thyroid cartilage, and as low 

 as the sixth ring of the trachea. 



From the upper border of the thyroid body, a conical process, 

 known as the pyramid, often ascends towards the hyoid bone, to 

 which it is attached by a fibrous band. The pyramid generally 

 springs from the inner part of one of the lateral lobes, seldom from 

 the isthmus ; and it is sometimes connected to the hyoid bone by a 

 slip of muscle, the levator glandulce thyroidecc. Detached portions of 



