MUSCLES DEPRESSING THE HYOID BONE. 191 



passes downwards and forwards, it is inserted aponeurotically into the pos- 

 terior part of the soft palate, and meets its neighbour of the opposite side. 

 In its upper part it is placed above the concave margin of the superior 

 constrictor. 



The circumflexus or tensor palati arises from the navicular fossa at the 

 root of the internal pterygoid plate, from the outer side of the Eustachian 

 tube, from the spine of the sphenoid, and the edge of the tympanic plate of 

 the temporal bone. It descends perpendicularly, resting on the internal 

 pterygoid plate, between it and the internal pterygoid muscle, and ends in 

 a tendon which, winding round the hamular process, lubricated by a bursa, 

 extends horizontally inwards, and terminates in the forepart of the aponeu- 

 rosis of the soft palate and the posterior border of the palate bone. 



ACTIONS. The muscles of the pharynx and soft palate are so arranged as to 

 accomplish, in conjunction with those of the tongue and hyoid bone, the action of 

 deglutition that is to say, the propulsion of food into the oesophagus without any 

 portion being permitted to pass into the nasal cavity or larynx. While the tongue 

 near the fauces is thrown upwards and backwards by the stylo-glossi muscles, and the 

 larynx is drawn upwards and forwards under it by muscles attached to the hyoid-bone, 

 and by the stylo-pharyngeus muscle, so as to be both closed by the epiglottis and 

 overlapped by the tongue, the palato-glossi muscles constrict the fauces and shut off 

 the bolus from the mouth. The soft palate is raised and made tense by its superior 

 muscles ; the palato-phary ngei, being approximated, nearly touch one another (the uvula 

 lying in the small interval between them), and prevent the passage of the food towards 

 the upper part of the pharynx or the posterior nares, while at the same time they form 

 an inclined surface for its guidance into the lower part of the pharynx. The food 

 being thus thrown into the grasp of the constrictors of the pharynx, those muscles 

 contract from above downwards and force it into the tube of the gullet below. 



MUSCLES DEPRESSING THE HYOID BONE. 



The sterno-hyoid muscle, a flat band of longitudinal fibres, arises variously, 

 from the sternum and the posterior sterno-clavicular ligament, from the 

 clavicle and that ligament, or from the clavicle only, and occasionally, to a 

 small extent, from the cartilage of the first rib. It is inserted into the lower 

 border of the body of the hyoid bone. 



The muscle is concealed below by the sternum and the sterno-mastoid, 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 corre- 

 sponding 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. 



The sterno-thyroid, broader and shorter than the preceding muscle, behind 

 which it lies, arises from the thoracic surface of the first bone 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. 



The greater 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 surface it rests on 

 the innominate vein, the lower part of the common carotid artery, the trachea, and 

 the thyroid 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. 



This muscle is often partly crossed by transverse or oblique tendinous lines. At 



