SUPERFICIAL CERVICAL REGION. 43 



The sterno-hyoid is to be divided and its two ends are to be re- 

 flected. In separating the steruo-hyoid and the thyro-hyoid muscles 

 on the median line the student should observe their relations with the 

 trachea and the isthmus of the thyroid gland, these being parts con- 

 cerned in the operation of tracheotomy. 



The STERNO-THYROID MUSCLE arises also from the tho- 

 racic surface of the first bone of the sternum, but lower 

 down than the preceding muscle: it is inserted into the 

 oblique line of the thyroid cartilage of the larynx ; it is 

 broader than the stern o-li} 7 oid, and, like that, is occasionally 

 marked by tendinous intersections. 



The THYRO-HYOID MUSCLE is a short muscle arising from 

 the oblique line of the thyroid cartilage and inserted into 

 the lower border of the body and cormi of the hyoid bone. 

 The separation between this muscle and the sterno-thyroid 

 is not always distinct ; normally they are separated by a 

 tendinous interval at the point where they are attached to 

 the oblique line of the thyroid cartilage, but it not unfre- 

 quently happens that even this is not sufficiently marked 

 to be apparent. 



The sterno-thyroid muscle is to be divided, and its ends reflected, 

 so as to expose the thyroid body. 



Between the common carotid arteries and upon the tra- 

 chea lies the THYROID BODY ; this is a dark red and vascu- 

 lar organ composed of two lobes, one on each side of the 

 trachea and larynx, connected by a narrow portion called 

 the isthmus, and which lies across the upper two or three 

 rings of the trachea ; the lobes are triangular in shape, their 

 bases being directed downward. It is well supplied with 

 arteries, receiving one from each external carotid, called 

 the superior thyroid, distributed to the upper part of the 

 lobes, and one from each thyroid axis of the subclavian, 

 called the inferior thyroid, which supplies the lower part 

 of the lobes ; occasionally there is a middle thyroid artery 

 sent to it from the arteria innominata ; all these arteries 

 anastomose freely with each other. When the middle thy- 

 roid is present, it usually lies upon the trachea in the me- 

 dian line, and may be a source of embarrassment in the 

 operation of tracheotomy. A small muscle called the leva- 

 tor glandulse thyroidese is sometimes found connected with 

 the upper border of one lobe or with the isthmus, and 

 attached to the hyoid bone ; it is said to be most frequent 

 on the left side, and its place is sometimes supplied by a 

 small lobule of glandular tissue, which is then called the 

 pyramid, or middle lobe. 



