392 



Nerves. The anterior belly of the Digastric is supplied by the mylohyoid branch of the 

 inferior dental; its posterior belly, by the facial; the Stylohyoid is supplied by the facial; the 

 Mylohyoid, by the mylohyoid branch of the inferior dental; the Geniohyoid, by a branch from 

 the ansa cervicalis which accompanies the hypoglossal in a common sheath. 



Actions. This group of muscles performs two very important actions. They raise the hvoid 

 bone, and with it the base of the tongue, during the act of deglutition; or, when the hyoid bone 

 is fixed by its Depressors and those of the larynx, they depress the mandible. During the first 

 act of deglutition, when the mass is being driven from the mouth into the pharynx, the hyoid bone, 

 and with it the tongue, is carried upward and forward by the anterior belly of the Digastric, 

 the Mylohyoid, and Geniohyoid muscles. In the second act, when the mass is passing through 

 the pharynx, the direct elevation of the hyoid bone takes place by the combined action of all 

 the muscles; and after the food has passed, the hyoid bone is carried upward and backward 

 by the posterior belly of the Digastric and Stylohyoid muscles, which assist in preventing the 

 return of the bolus into* the mouth. 



4. The Lingual Region (Figs. 303, 304). 



Geniohyoglossus. Styloglossus. 



Hyoglossus. Palatoglossus. 1 



Chondroglossus. 



Dissection. After completing the dissection of the preceding muscles, saw through the 

 mandible just external to the symphysis. Then draw the tongue forward, and attach it, by a 

 stitch, to the nose; when its muscles, which are thus put on a stretch, may be examined. 



The Geniohyoglossus (TO. genioglossus) has received its name from its triple 

 attachment to the mandible, hyoid bone, and tongue. It is a flat, triangular 

 muscle, placed vertically on either side of the middle line, its apex corresponding 

 with its point of attachment to the mandible, its base with its insertion into the 

 tongue and hyoid bone. It arises by a short tendon from the superior genial 

 tubercle on the inner side of the symphysis of the mandible, immediately above 

 the Geniohyoid; from this point the muscle spreads out in a fan-like form, a few 

 of the inferior fibres passing downward, to be attached by a thin aponeurosis 

 into the upper part of the body of the hyoid bone, a few fibres passing between 

 the Hyoglossus and Chondroglossus to blend with the Constrictor muscles of 

 the pharynx; the middle fibres passing backward, and the superior ones upward 

 and forward, to enter the whole length of the under surface of the tongue, from 

 the base to the apex. The two muscles lie on either side of the median plane; 

 behind they are quite distinct from each other, and are separated at their insertion 

 into the under surface of the tongue by a tendinous raphe, which extends through 

 the middle of the organ. In front the two muscles are more or less blended; 

 distinct fasciculi are to be seen passing off from one muscle, crossing the middle 

 line, and intersecting with bundles of fibres derived from the muscle on the other 

 side. 



Relations. By its deep surface this muscle is in contact with its fellow of the opposite side; 

 by its superficial surface, with the Inferior lingualis, the Hyoglossus, the lingual artery and 

 hypoglossal nerve, the lingual nerve, and sublingual gland; by its upper border, with the mucous 

 membrane of the floor of the mouth (frenum linguae) ; by its lower border with the Geniohyoid. 



The Hyoglossus (TO. hyoglossus) is a thin, flat, quadrilateral muscle which 

 arises from the side of the body and whole length of the greater cornu of the 

 hyoid bone, and passes almost vertically upward to enter the side of the tongue, 

 between the Styloglossus and Lingualis. The fibres of this muscle which arise 



1 The Palatoglossus, or constrictor isthmi faucium, although one of the muscles of the tongue which serves 

 to draw the base of that organ upward during the act of deglut'tion, is more nearly associated, both in situation 

 and function, with the soft palate. It will consequently be described with the group of Palatal muscles. 



