THE MUSCLES OF THE HEAD. m 



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. 



Insertion. 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 (d) and medialis ($). Inner surface with 

 the skull, the ptejygoideus externus (Fig. 66, <), and the struc- 

 tures within the orbit. 



Action. Elevator of the lower jaw. 



M. pterygoideus externus (Fig. 66, b). This lies on the 

 medial side of the mandible, ventrad of the ventral portion of 

 the temporal. 



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 (#), 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, s). 



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 



