TEMPORAL AND INFRATEMPORAL REGIONS 269 



Musculus Pterygoideus Interims. The internal pterygoid 

 also is bicipital at its origin, and its two heads embrace the 

 origin of the lower head of the external pterygoid. The 

 superficial and smaller head of the internal pterygoid springs 

 from the lower and posterior part of the tuberosity of the 

 maxilla, and also from the lateral surface of the pyramidal 

 process (O.T. tuberosity) of the palate bone ; the deep head, 

 hidden by the external pterygoid, arises in the pterygoid 

 fossa from the medial surface of the lateral pterygoid lamina, 

 and from the surface of the pyramidal process of the palate 

 bone which appears between the two pterygoid laminae. 

 The two heads of the muscle unite at the lower margin of the 

 anterior part of the external pterygoid, and the fibres proceed 

 downwards with a postero - lateral inclination and gain 

 insertion into the angle of the mandible, and into the lower 

 and posterior part of the medial aspect of the ramus as 

 high as the mandibular foramen. 



Arteria Maxillaris Interna. This vessel is the larger of 

 the two terminal branches of the external carotid artery. It 

 takes origin immediately posterior to the neck of the 

 mandible and proceeds anteriorly to the anterior part of the 

 infratemporal fossa, where it disappears from view by dipping 

 between the two heads of origin of the external pterygoid 

 muscle and entering the pterygo-palatine fossa. It is 

 divided into three parts for convenience of description. The 

 first part runs horizontally between the neck of the mandible 

 and the spheno-mandibular ligament. It lies along the 

 lower border of the posterior part of the external pterygoid 

 muscle, and usually crosses the inferior alveolar nerve super- 

 ficially. The second part extends obliquely upwards and 

 anteriorly upon the lateral surface of the external pterygoid 

 muscle, under cover of tne insertion of the temporal muscle. 

 The third part dips between the two heads of the external 

 pterygoid into the pterygo-palatine fossa. 



This is the most frequent arrangement, but it is not 

 uncommon to find the second part of the artery lying in a 

 deeper plane, viz. between the internal and external pterygoid 

 muscles. In that case the vessel makes a bend laterally 

 between the heads of the external pterygoid muscle, and 

 appears on its surface before entering the pterygo-palatine 

 fossa. 



The branches of the internal maxillary artery are classified 



