244 HEAD AND NECK 



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. 



Musculus Sternothyreoideus. This muscle lies under cover 

 of the preceding and is both broader and 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. An 

 incomplete tendinous intersection may sometimes be noticed 

 interrupting its muscular fibres. The nerve supply is derived 

 from the ansa hypoglossi. 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. 



Musculus Thyreohyoideus. This 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 outer surface of the lamina of the thyreoid cartilage, 

 and is inserted into the lower border of the great 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 internal laryngeal 

 nerve enter the pharynx. It is supplied by a twig from the 

 hypoglossal nerve. 



Dissection. The dissectors of the head and neck should now proceed to 

 study the relations of the common carotid and subclavian arteries, the 

 cervical part of the thoracic duct, and the dome of the pleura, before these 

 are disturbed by the dissectors of the thorax. Whilst this is being done, 

 the omo-hyoid must be retained in position, but the upper and lower portions 

 of the other infra-hyoid muscles may be turned upwards and downwards 

 respectively. 



Remove the remains of the fascial sheath from around the common 



