CHAP. VI.] 



THE MUSCLES. 



61 



FIG. 57. MUSCLES OF THE TONGUE. 



The chief muscles connecting the tongue and tongue bone to 

 the lower jaw are the genio-glossus and stylo-glossus. They are 

 interesting to us from the fact that during general ansesthesia 

 they, together with the other muscles, become relaxed, and it 

 is necessary to press the angle 

 of the lower jaw upwards and 

 forwards in order to prevent 

 the tongue from falling back- 

 wards and obstructing the 

 larynx. 



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. 

 It serves as a convenient landmark in locating the great vessels 

 carrying the blood to and from the head. If one of these 

 muscles be either abnormally contracted or paralyzed, we get 

 the deformity called wry neck. 



The muscles of the trunk may be arranged in three groups : 

 (1) muscles of the back; (2) muscles of the thorax; (3) muscles 

 of the abdomen. 



The muscles of the back are disposed in five layers, one be- 

 neath another. The two largest and most superficial are the 

 trapezius and the latissimus dor si. 



The trapezius arises from the middle of the occipital bone, 

 from the ligamentum nuchce, and from the spinous processes of 

 the last cervical and all the dorsal vertebrae. From this ex- 

 tended line of origin the fibres converge to their insertion in 

 the acromion process and spine of the scapula. The latissimus 

 dorsi arises from the last six dorsal vertebrae, and through the 

 medium of the lumbar aponeurosis, from the lumbar and sacral 

 part of the spine and from the crest of the ilium. The fibres 

 pass upwards and converge into a thick, narrow band, which 



