THE PTERYGO-MAXILLARY REGION. 



405 



internal maxillary artery, which crosses it, 1 the tendon of the Temporal muscle, 

 and the Masseter : by its internal surface it rests against the upper part of the 

 Internal pterygoid. the internal lateral ligament, the middle meningeal artery, 



FIG. 274. The Pterygoid muscles, the zygomatic arch and a portion of the ramns of the jaw having been 

 removed. 



and inferior maxillary nerve : by its upper border it is in relation with the temporal 

 and masseteric branches of the inferior maxillary nerve ; by its lower border it is 

 in relation with the inferior dental and gustatory nerves, and it is pierced by^the 

 buccal nerve. In the interval between the two portions of the muscle the internal 

 maxillary artery passes, when this vessel lies on the muscle (see Fig. 274). 



The Internal Pterygoid is a thick, quadrilateral 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 tuberosity 

 of the palate bone and from the tuberosity of the superior maxillary bone ; 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 lower jaw. as high as the dental foramen. 



Eelations. By its external surface, with the ramus of the lower jaw, from 

 which it is separated, at its upper part, by the External pterygoid, the internal 

 lateral ligament, the internal maxillary artery, the dental vessels and nerves, and 

 the lingual nerve : by its internal nor/ace^ with the Tensor palati, being separated 

 from the Superior constrictor of the pharynx by a cellular interval. 



Nerves. These muscles are supplied by the inferior maxillary nerve. 



Actions. The Temporal and Masseter and Internal pterygoid raise the lower 

 jaw against the upper with great force. The superficial portion of the Masseter 

 assists the External pterygoid in drawing the lower jaw forward upon the upper, 

 the jaw being drawn back again by the deep fibres of the Masseter and posterior 

 fibres of the Temporal. The External pterygoid muscles are the direct agents in 

 the trituration of the food, drawing the lower jaw directly forward, so as to make 

 the lower teeth project beyond the upper. If the muscle of one side acts, the 

 corresponding side of the jaw is drawn forward, and, the other condyle remaining 

 fixed, the symphysis deviates to the opposite side. The alternation of these 

 movements on the two sides produces trituration. 



1 This is the usual relation, but in many cases the artery will be found below the muscle 



