172 HEAD AND NECK 



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 behind the last molar tooth, and also from the adjoin- 

 ing 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 posterior 

 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. The internal pterygoid raises the mandible, pro- 

 trudes it, and pulls it towards the opposite side. It is 

 supplied by a branch of the mandibular division of the tri- 

 geminal nerve. 



Arteria Maxillaris Interna. The internal maxillary artery 

 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 passes forwards 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 

 forwards upon the lateral surface of the lower head of the 

 external pterygoid muscle, under cover of the insertion of the 

 temporal muscle. The third part dips between the two heads 

 of the external pterygoid into the pterygo-palatine fossa 

 (Fig- 63). 



The arrangement described is that most frequently found, 

 but it is not uncommon to find the second part of the artery 

 lying in a deeper plane, viz. between the internal and external 



