THE MUSCLES OF THE HEAD. 113 



the superficial surface of the digastric, caudad and ventrad of 

 the angle of the jaw. 



Origin by fleshy fibres from the outer surface of the stylohyal 

 bone near its middle. The muscle curves over the outer sur- 

 face of the digastric (^), and ends about one centimeter from 

 the middle line in a slender flat tendon. 



Insertion into the middle of the ventral surface of the body 

 of the hyoid bone. Some of the fibres of the mylohyoid (c) are 

 inserted into its tendon. 



Relations. Outer surface with the submaxillary gland (2) 

 and the submentalis muscle. Inner surface with the digastric (<), 

 the hyoglossus (Fig. 67, //), and the geniohyoid (Fig. 67, g). 



Action. Raises the hyoid. 



M. geniohyoideus (Fig. 67, g). The geniohyoid is a long 

 slender muscle which lies next to the median line between the 

 symphysis menti and the hyoid bone, closely applied to its 

 fellow of the opposite side and within (dorsad of) the mylohyoid 

 (Fig. 65, c}. 



Origin from the ventral half of the inner surface of the 

 mandibula for about one millimeter from the symphysis. 



Insertion by muscle-fibres into the lateral half of the ventral 

 surface of the body of the hyoid bone. 



Relations. Outer (ventral) surface with the stylohyoid 

 (Fig. 65, d] and the mylohyoid (Fig. 65, c); medial border with 

 the muscle of the opposite side. Lateral border with the 

 hyoglossus (Fig. 67, //) and genioglossus (Fig. 67, /). Inner 

 (dorsal) surface with the genioglossus. 



ActioJi. Draws the hyoid forward. 



M. jugulohyoideus (Fig. 67, ). The jugulohyoid is a 

 small flat quadrangular muscle covering the outer part of the 

 ventral surface of the tympanic bulla. 



Origin from the ventral border of the jugular process. 



Insertion into the caudal side of the cartilaginous part of the 

 stylohyoid opposite the origin of the styloglossus. 



Relations. Ventral surface with the digastric. Dorsal sur- 

 face with the tympanic bulla (s). 



Action. Draws the hyoid backward and thus gives a firmer 

 surface of origin for the styloglossus. 



