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 (4), 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 (0), 
the hyoglossus (Fig. 67, 2), and the geniohyoid (Fig. 67, g). 
Action.—Raises the hyoid. 
M. geniohyoideus (Fig. 67, ¢).—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, ¢). 
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, f). Inner 
(dorsal) surface with the genioglossus. 
Action.—Draws the hyoid forward. 
M. jugulohyoideus (Fig. 67, 4).—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 (3). 
Action.—Draws the hyoid backward and thus gives a firmer 
surface of origin for the styloglossus. 
