THE MUSCLES OF THE HEAD. TIT 
poral fossa, except in cases where the cranial part of the fossa 
is occupied by the superficial portion. The fibres converge 
toward the coronoid process, and the ventral third of the outer 
surface is covered by strong fascia. 
/nsertion.—The whole inner surface of the coronoid process 
of the mandible. 
Relations.—Outer surface with the external ear, the ear- 
muscles (Fig. 63), the epicranius (Fig. 63, %), the corrugatores 
supercilii lateralis (7) and medialis (4). Inner surface with 
the skull, the pterygoideus externus (Fig. 66, 4), and the struc- 
tures within the orbit. 
Action.—Elevator of the lower jaw. 
M. pterygoideus externus (Fig. 66, 4).—This lies on the 
medial side of the mandible, ventrad of the ventral portion of 
the temporal. 7 
Origin.—The external pterygoid fossa (Fig. 40, £), which 
lies on the lateral surface of the perpendicular plate of the pala- 
tine bone, and on the surface of the pterygoid process of the 
sphenoid bone dorsad of the internal pterygoid fossa. The 
fossa extends from the foramen rotundum to the sphenopala- 
tine foramen. The muscle passes with parallel fibres laterad, 
ventrad, and caudad and has its 
Insertion by a strong flat tendon into the medial surface of 
the mandible near its ventral border between the opening of 
the mandibular canal and the base of the angular process. 
Relations. —Ventral surface with the masseter (a), the 
digastric, and the soft palate with its muscles. Dorsal surface 
with the temporal, and near its origin with the muscles of the 
eye, and other structures in the orbit. 
Action.—Elevator of the lower jaw. 
M. pterygoideus internus (Fig. 66, c).—This lies caudad 
of the pterygoideus externus, nearly parallel to it, and is con- 
nected with it at its lateral end. 
Origin from the whole surface of the internal pterygoid 
fossa (Fig. 40, 5). 
Insertion by fleshy fibres into the ventral surface of the 
external pterygoid and its tendon, into the medial surface of 
the angular process of the mandible and caudad of the angular 
