INFKA-HYOID MUSCLES 



293 



occasionally, to a small extent, from the cartilage of the first rib. It is 

 inserted iuto the lower border of the body of the hyoid bone. 



Relations.— The muscle is concealed below by the sternum and the sterno- 

 mastoid muscle, higher up by the skin and fascia only ; it lies on the sterno-thyroid 

 and thyro-hyoid muscles, which it partly covers. The inner border approaches that 

 of the con-esponding muscle towards the middle of its extent, but is separated from 

 it by a slight interval superiorly, and by a larger interval near the sternum ; the 

 outer margin is in contact with the omo-hyoid near the os hyoides. The muscular 

 fibres are, in many cases, interrupted by a transverse tendinous intersection. 



Fig. 214. — View op the 



SuBMAXILLARVr MUSCLES 

 AND THE DeI'KESSORS OP 



THE Hyoid Bone and 

 Larynx, from before. 

 (After Bourgery). 3 



(For the explanation of 

 the references in the upper 

 jjart of the figure, see p. 

 282). c, body of the hjoid 

 bone ; d, mastoid process ; 

 c, placed on the front of 

 the thyroid cartihige, points 

 to the thyro-hyoid muscle ; 

 f, upper part of the ster- 

 num ; (J, lateral lobe of the 

 thyroid gland ; + , its isth- 

 mus, above which is the cri- 

 coid cartilage covered by the 

 crico-thyroid muscle ; 8, 

 placed on the levator sca- 

 pulae, jjoints to the left 

 middle constrictor of the 

 pharynx ; 9, placed on the 

 middle scalenus, points to 

 the left inferior constrictor ; 

 10, right sterno -hyoid ; 11, 

 jilaced on the left sterno- 

 thyroid, j)oints also to the 

 lower part of the right mus- 

 cle ; 12, placed on the right sterno-raastoiil, points to the upper and lower bellies of 

 the right omo-hyoid. 



Tlie sterno-thyroid, broader and shorter than the preceding muscle, 

 behind which it lies, arises from tlie thoracic sl^rface of the first part of 

 the sternum, lower down and more internally than the sterno-hyoid 

 muscle, and ascends, diverging a little from its fellow, to be inserted 

 into the oblique line on the ala of the thyroid cartilage. 



Jielation.i. — The gi-eater part of its anterior surface is concealed by the .sternum 

 and the sterno-hyoid muscle, as well as by the sterno-mastoid. By its deep sur- 

 face it rests on the innominate vein, the lower part of the common carotid artery, 

 the trachea, and the thyi-oid body. The inner margin is contiguous to the 

 muscle of the other side in the lower part of the neck. The median incision in 

 the operation of tracheotomy is made between the two muscles. 



Varii'tu'.s. — This muscle is sometimes partly crossed by transverse or oblique 

 tendinous lines. At the ujaper extremity a few fibres are often found to blend 

 with the thjTO-hyoid muscle or with the inferior constrictor of the pharjoix. 



The thyro-hyoid muscle is continued upwards from the preceding ; 

 it arises from the oblique line on the ala of the thyroid cartilage, and. 



