_Insertion.-_-The outer surface of the coronoid process of the mandible dorsad of the coronoid fossa, and both borders of the coronoid process. The cranial fibres may be inserted craniad of the coronoid process onto the aponeurosis covering the deep portion of the muscle. The caudal part of this portion is more or less distinct and is sometimes described as a separate head. The =deep portion=. _Origin_ by fleshy fibres from the whole surface of the temporal 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, _h_), the corrugatores supercilii lateralis (_d_) and medialis (_b_). Inner surface with the skull, the pterygoideus externus (Fig. 66, _b_), and the structures 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, _h_), which lies on the lateral surface of the perpendicular plate of the palatine 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 sphenopalatine 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 connected 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 process for about one centimeter into a fascia common to it and the masseter muscle, and into the stylomandibular ligament. [Illustration: FIG. 66.--OBLIQUELY VENTRAL VIEW OF THE DEEP MUSCLES OF THE LOWER JAW AND PALATE.