476 



HUMAN ANATOMY. 



Relations. — Superficial to the temporal fascia are branches of the superficial 

 temporal vessels and the auriculo-temporal nerve. Beneath, the muscle is in relation 

 to the internal maxillary artery and the external pterygoid muscle. 



3. Pterygoideus Externus (Fig. 496). 



Attachments. — The external pterygoid arises by two heads. The upper 

 head takes its origin from the under surface of the great wing of the sphenoid, inter- 

 nal to the infratemporal crest (pterygoid ridge), while the lower head arises from 

 the outer surface of the lateral pterygoid plate. The two heads are at first separated 

 by a narrow triangular interval through which the internal maxillary artery passes, 

 but, passing backward and outward, they soon unite to be inserted into the anterior 

 border of the interarticular fibro-cartilage of the mandibular articulation and into the 



neck of the condyloid process of the 



Fig. 496. 



Temporal bone (cut) 



— < ' ndyle of 

 mandible 



head) External 

 d J pterygoid 



mandible. 



Nerve-Supply. — By the exter- 

 nal pterygoid branch of the anterior 

 portion of the mandibular division of 

 the trigeminus. 



Action. — When both muscles 

 act together, they draw the jaw and 

 the interarticular fibro-cartilage for- 

 ward, a movement which always 

 accompanies and assists in the de- 

 pression of the jaw. When but one 

 muscle acts, the ramus to which it is 

 attached is drawn forward, while the 

 other pivots in its articular surface, 

 the result being an apparent lateral 

 movement of the jaw towards the 

 pivotal side. 



Relations. — The outer surface 

 of the external pterygoid is in rela- 

 tion to the coronoid process of the 

 mandible and the temporal muscle, 

 its lower head is frequently crossed by the internal maxillary artery and the buccal 

 nerve, and anteriorly it is separated from the masseter by the buccal fat-pad. The 

 deep surface rests upon the upper part of the internal pterygoid muscle, and is in 

 relation to the internal maxillary artery and the inferior dental and lingual branches 

 of the mandibular division of the trigeminus. 



Internal pterygoid 



Mylo-hyoid, stump 

 External and internal pterygoid muscles, seen from within. 



4. Pterygoideus Internus (Fig. 496). 



Attachments. — The internal pterygoid arises from the walls and floor of the 

 pterygoid fossa, the majority of its fibres being attached to the inner surface of the 

 external pterygoid plate and to the tuberosity of the palate bone. A smaller bundle 

 of fibres, forming what may be termed a second head, separated from the main por- 

 tion of the muscle by the lower head of the external pterygoid, frequently arises 

 from the tuberosity of the maxilla and the adjacent portion of the palate bone. 

 From these origins the fibres are directed downward and somewhat outward and 

 backward to be inserted into the inner surface of the angle and ramus of the mandi- 

 ble below the mylo-hyoid groove. 



Nerve-Supply. — By the internal pterygoid branch from the trunk of the 

 mandibular division of the trigeminus. 



Action. — Its chief action is to raise the jaw, having in this respect almost as 

 powerful action as the masseter. Owing to the direction of its fibres, it will also 

 assist the external pterygoid in protruding the jaw and in producing its lateral 

 movements. 



Relations. — The outer surface of the muscle is in relation with the ramus ot 

 the mandible, the internal maxillary artery, and the inferior dental and lingual nerves 



