Chap. VII] MUSCULAR TISSUE 101 



converge to the angle of the mouth, and are inserted into the 

 orbicularis oris. 



Action. — It compresses the cheeks, helps to close the mouth, 

 and assists in such motions as blowing a trumpet. 



Chief muscles of the tongue. — The chief muscles connecting 

 the tongue and hyoid bone to the lower jaw are the genioglossus 

 and the styloglossus, 



Genioglossus. — The genioglossus has its origin in the front part 

 of the mandible, and is inserted in the whole length of the tongue 

 in and at the side of the mid line. 



Actioii. — ■ It thrusts the tongue forward, retracts it, and also 

 depresses it. 



Styloglossus. — The styloglossus has its origin in the styloid 

 process ^ of the temporal bone, and is inserted in the whole length 

 of the side and under part of the tongue. 



Action. — It draws the tongue backward. 



These muscles are interesting to us from the fact that during 

 general anaesthesia they, together with the other muscles, become 

 relaxed, and it is necessary to press the angle of the lower jaw 

 upward and forward in order to prevent the tongue from falling 

 backward and obstructing the larynx. 



Muscles of the neck. — The two superficial muscles of the 

 neck are: (1) platysma, (2) sterno-cleido-mastoid. 



Platysma (broad sheet muscle) . — It arises from the skin and 

 areolar tissue covering the pectoral, deltoid, and trapezius muscles, 

 and is inserted in the mandible and muscles about the angle of 

 the mouth. 



Action. — It draws the angle of the mouth down and contracts 

 the skin of the neck. 



Sterno-cleido-mastoid. — The most prominent muscle of the 

 neck is the sterno-cleido-mastoid. It is named from its origin 

 and insertion, arising from part of the sternum and clavicle, and 

 being inserted into the mastoid portion of the temporal bone. 

 This muscle is easily recognized in thin persons by its forming a 

 cord-like prominence obliquely situated along each side of the neck. 



Action. — Both sterno-cleido-mastoid muscles acting together 

 flex the head on the chest or neck. They serve as convenient 

 landmarks in locating the great vessels carrying the blood to and 



1 See Fig. 27. 



