” 
108 THE MUSCLES. 
Jnsertion.—The ventral border of the mandible craniad of 
the caudal border of the molar tooth. The insertion area 
extends slightly onto both surfaces of the bone and.is triangular, 
with its apex craniad. 
Relations.—-Outer (ventral) surface with the following, 
beginning at the caudal end: the rectus capitis lateralis, the 
cleidomastoid (4), the submaxillary gland (2), the stylohyoid 
(2), a large lymph-gland (3), and the integument. Inner 
(dorsal) surface with the jugulohyoid, the tympanic bulla, the 
masseter (a), the hyoglossus, and the mylohyoid (c). 
Action.—Depressor of the lower jaw. 
M. masseter (Figs. 65 and 66, a).—The masseter forms 
the projecting mass so prominent in the cat behind and below 
the eye. Its outer surface is covered by a strong aponeurosis. 
The muscle is divided into three layers which are distinct as 
to origin, insertion, and direction of fibres, but which are 
otherwise not distinct. 
The superficial layer takes 
Origin by the superficial aponeurosis from the ridge which 
runs lengthwise of the outer surface of the malar bone, and by 
fleshy fibres from the surface of the malar bone ventrad of this 
ridge. The fibres pass obliquely caudad to their insertion. 
Insertion.—The caudal half of the lateral margin of the 
ventral border of the mandible, by a sheet of fascia which lies 
on the inner surface of the muscle. The superficial fibres curve 
ventrad of the mandible and are inserted into a tendinous inter- 
section between this muscle and the internal pterygoid (Fig. 
66, ¢). 
The middle layer takes 
Origin from the ventral border of the malar bone, from 
opposite the molar tooth to within three millimeters of the 
mandibular fossa. The fibres pass ventrad and have their 
lusertion into the mandible at the ventral border of the 
external coronoid fossa by means of the aponeurosis which 
covers the inner surface of the muscle. 
The deep layer takes 
Origin by a strong tendon from the ventral border of the 
zygoma just craniad of the mandibular fossa. The fibres pass 
cranioventrad, diverge and have their 
