146 HEAD AND NECK 



below its insertion it covers part of the thyreo-hyoid 

 membrane. Both bellies are supplied by branches from the 

 ansa hypoglossi. Acting from the scapula it pulls the hyoid 

 bone downwards and slightly backwards. 



Musculus Sternohyoideus. The sterno-hyoid muscle arises 

 from the posterior aspect of the medial end of the clavicle, 

 the posterior sterno-clavicular ligament, and the posterior 

 surface of the manubrium sterni. It is inserted into the 

 lower border of the body of the hyoid bone, between the 

 median plane and the insertion of the omo-hyoid. A short 

 distance above the sternum an oblique tendinous intersection 

 frequently divides it into two portions. The lower part of 

 the muscle is covered by the sterno-mastoid, and it is crossed 

 by the anterior jugular vein. Its principal deep relations are 

 the lower part of the common carotid artery and the sterno- 

 thyreoid muscle, which separates it from the lateral lobe of 

 the thyreoid gland. It is supplied by branches from the 

 ansa hypoglossi. It pulls the hyoid bone downwards. 



Musculus Sternothyreoideus. The sterno-thyreoid muscle 

 lies under cover of the preceding and is broader but shorter. 

 It springs from the posterior aspect of the manubrium sterni 

 and from the cartilage of the first rib. Diverging slightly 

 from its fellow as it ascends, it is inserted into the oblique 

 line on the lateral face of the lamina of the thyreoid cartilage, 

 parallel with and immediately below the thyreo-hyoid. An 

 incomplete tendinous intersection may sometimes be noticed 

 interrupting its muscular fibres. In the neck, it is covered 

 in the greater part of its extent by the sterno-hyoid ; but the 

 posterior part of its insertion is covered by the anterior belly 

 of the omo-hyoid ; and the lower and anterior part is covered 

 by skin and fascia only. The nerve supply is derived from the 

 ansa hypoglossi. It pulls the thyreoid cartilage downwards. 



Musculus Thyreofiyoideus. The thyreo-hyoid muscle lies 

 on the same plane as the sterno-thyreoid, and may be 

 regarded as its upward continuation. It takes origin from 

 the oblique line on the lateral surface of the lamina of the 

 thyreoid cartilage, and is inserted into the lower border of the 

 greater cornu of the hyoid bone, under cover of the omo- 

 hyoid muscle. It conceals part of the lamina of the 

 thyreoid cartilage and the lateral part of the thyreo-hyoid 

 membrane, and the aperture in the membrane through which 

 the laryngeal branch of the superior thyreoid artery and the 



