380 



THE MUSCLES AND FASCIA 



The Internal pterygoid muscle (ra. pterygoideus internus] is a thick, quadri- 

 lateral muscle, and resembles the Masseter in form. It arises from the pterygoid 

 fossa, being attached to the inner surface of the external pterygoid plate and to 

 the grooved surface of the tuberosity of the palate bone, and by a second slip 

 from the outer surface of the tuberosities of the palate and maxilla: its fibres pass 

 downward, outward, and backward, to be inserted, by a strong, tendinous lamina, 

 into the lower and back part of the inner side of the ramus and angle of the 

 mandible as high as the dental foramen. 



FIG. 298. The Pterygoid muscles, viewed from behind, the buck portion of the skull having been removed. 



(Testut.) 



Relations. By its superficial surface, with the ramus of the mandible, from which it is sep- 

 arated, at its upper part, by the External pterygoid muscle, the internal lateral ligament, the 

 internal maxillary artery, the dental vessels and nerves, and the lingual nerve, and a process 

 of the parotid gland. By its deep surface, with the Tensor palati, being separated from the 

 Superior constrictor of the pharynx by a cellular interval. 



Nerves. These muscles are supplied by branches of the inferior maxillary division of the 

 trigeminal nerve. 



Actions. The Temporal, Masseter, and Internal pterygoid raise the mandible against the 

 maxillse with great force. The External pterygoids assist in opening the mouth, but their main 

 action is to draw forward the condyles and articular disks so that the mandible is protruded and the 

 inferior incisors are projected in front of the upper ; in this action they are assisted by the Internal 

 pterygoids. The mandible is retracted by the posterior fibres of the Temporal. If the Internal 

 and External pterygoids of one side act, the corresponding side of the mandible is drawn for- 

 ward, while the opposite condyle remains comparatively fixed, and lateral movement, such as 

 occurs during the trituration of the food, takes place. 



Surface Form. The outline of the muscles of the head and face cannot be traced on the 

 surface of the body, except in the case of two of the masticatory muscles. Those of the head 



