THE 1NFKA-HYOID Mt'srLKS. 585 



auricular and superficial cervical nerves. If the muscle be cut 

 through below and raised, it will be seen to lie on the following 

 parts : The clavicular origin is superficial to the anterior scalenus 

 and oino-hyoid muscles, the transverse cervical and suprascapular 

 arteries, and the phrenic nerve. The sternal head conceals the 

 depressors of the hyoid bone, and the common carotid artery with 

 its vein and nerves. After the union of the heads, the muscle is 

 placed over the cervical plexus, the middle scalenus, and the 

 elevator of the angle of the scapula ; and near the skull on the 

 digastric and splenius muscles, the occipital artery, and part of the 

 parotid gland. The spinal accessory nerve perforates the muscular 

 fibres about the junction of the upper and middle thirds. 



Action. Both muscles acting bend the cervical part of the spine, use. 

 carrying the head forwards ; but one muscle will turn the face to 

 the opposite side. In conjunction with other muscles attached to 

 the mastoid process, one sterno-uiastoid "will incline the head 

 towards the shoulder of the same side. 



In laborious respiration the two muscles will assist in elevating 

 the sternum. 



The OMOHYOID MUSCLE crosses beneath the sterno-mastoid, and Omo-hyoid 

 consists of two fleshy bellies united by a small intermediate tendon. t^n s e a t 

 The origin of the muscle from the scapula, and the relations of tlj e scapula, 

 the posterior belly have been studied in the dissection of the 

 back (p. 522). From the intervening tendon the anterior fleshy and ends at 

 belly (fig. 211, 3 ) is directed upwards along the outer border Jf hyoid bone: 

 the sterno-hyoid muscle, and is inserted into the lower border of 

 the body of the hyoid bone, close to the great cornu. 



The anterior beily is in contact with the fascia, after escaping relations ; 

 from beneath the sterno-mastoid, and rests on the sterno- thyroid 

 and thyro-hyoid muscles. This part of the muscle crosses the 

 carotid vessels on a level with the cricoid cartilage. 



Action. The onio-hyoid muscle depresses and tends to draw use. 

 backwards the hyoid bone. 



The STERNO-HYOID MUSCLE (fig. 211, 2 ) is a flat thin band nearer sterno- 

 the middle line than the preceding. It arises from the inner end 

 of the clavicle at its posterior aspect, from the back of the 

 manubrium and of the cartilage of the first rib. From this origin it 

 ascends to be in<$>:rtf! into the lower border of the body of the 

 hyoid bone, internal to the preceding muscle. Its fibres are often 

 interrupted near the clavicle by a tendinous intersection. 



One surface is covered 1 y the sterno-mastoid and the fascia, relations ; 

 When the muscle is divided and turned aside, the deep surface 

 will be found to rest on the sterno-thyroid, the thyro-hyoid, and the 

 thyroid cartilage. The right and left muscles are separated by an 

 interval which is wider below than above. 



Action. It draws the hyoid bone downwards after swallowing ; use. 

 and in laborious respiration it will aid in raising the sternum. 



The STERXO-THYROID MUSCLE is broader and shorter than the stemo- 

 steriio-hyoid, beneath which it lies. It arises from the posterior muscle: 

 surfaces of the sternum and the cartilage of the first rib below the 



