INFRA-HYOID REGION. 



335 



Thyro-hyoid muscles, the thyroid gland, the superior thyroid vessels, the crico- 

 thyroid and thyro-hyoid membranes. 



The Sterno-ihyroid is situated beneath the preceding muscle, but is shorter 

 and wider than it. It arises from the posterior surface of the first bone of the 

 sternum, below the origin of the Sterno-hyoid, and occasionally from the edge 

 of the cartilage of the first rib; and is inserted into the oblique line on the side 



Fig. 221. Muscles of the Neck. Anterior View. 



of the ala of the thyroid cartilage. This muscle is in close contact with its fel- 

 low at the lower part of the neck ; and is frequently traversed by a transverse 

 or oblique tendinous intersection, like those in the Kectus Abdominis. 



Variations. This muscle is sometimes continuous with the Thyro-hyoid and Inferior Con- 

 strictor of the pharynx ; and a lateral prolongation from it sometimes passes as far as the os 

 hyoides. 



Relations. By its anterior surface, with the Sterno-hyoid, Omo-hyoid, and 

 Sterno-mastoid. By its posterior surface, from below upwards, with the trachea, 

 vena innominata, common carotid (and on the right side the arteria innominata), 

 the thyroid gland and its vessels, and the lower part of the larynx. The mid- 

 dle thyroid vein lies along its inner border, a relation which it is important to 

 Temember in the operation of tracheotomy. 



The Thyro-hyoid is a small quadrilateral muscle appearing like a continuation 

 of the Sterno-thyroid. It arises from the oblique line on the side of the thyroid 

 cartilage, and passes vertically upwards to be inserted into the lower border 

 of the body and greater cornu of the hyoid bone. 



Relations. By its external surface, with the Sterno-hyoid and Omo-hyoid 

 muscles. By its internal surface, with the thyroid cartilage, the thyro-hyoid 

 membrane, and the superior laryngeal vessels and nerve. 



The Omo-hyoid passes across the side of the neck, from the scapula to the 

 hyoid bone. It consists of two fleshy bellies, united by a central tendon. It 



