PTERYG OIDEUS EXTERXUS 



443 



and much stronger head is at first separated from the upper by a small chink, 

 which may give passage to the internal maxillary vessels. It arises fleshy, con- 

 verges backwards, outwards, and somewhat upwards, and is inserted by short 

 tendinous fibres. 



Nerve-supply. — Th{» external pterygoid branch of the motor portion of the 

 mandibular division of the fifth nerve, which divides into filaments entering its 

 deep surface. 



Action. — (1) To draw forwards the ramus of the mandible, and the inter- 

 articular fibro-cartilage; (2) to draw them inwards. The combination of these 

 two movements produces the oblique movement of the lower molar teeth of one 

 side forwards and inwards with respect to the upper molars which are their 

 opponents. It should be observed also that this inward movement of one side is 

 the action by which the ramus of the opposite side is moved outwards. (3) To 

 assist in opening the mouth by depression of the lower jaw. As the transverse 

 axis of this movement passes through the mandible at two points situated below 



Fig. 313. — The Pterygoid Muscles. 



|'4 'j ' Interartioular fibro-cartilage 



External pterygoid 



Internal pterygoid 



the necks of the rami, it follows that a forward movement of the condyles and 

 necks will assist in the backward movement of the angles and body which accom- 

 panies the depression of the mandible. 



Relations. — Superficially, the anterior fibres of the internal pterygoid, the 

 temporal muscle, and, at a little distance, a small part of the masseter; deeply, the 

 internal pterygoid muscle, the internal maxillary vessels (unless, as sometimes, 

 they pass across the outer surface of the lower head), the middle meningeal and 

 inferior dental vessels, with the masseteric and posterior deep temporal nerves 

 passing behind or through the attachment of the upper head; the buccal and ante- 

 rior deep temporal ners'es running V)etweeii the two heads; the lingual gustatory 

 and inferior dental nerves beneath the lower head. 



Variations. — Muscular fibres are froqueiitlj' found upon the deep surface of the external 

 pterygoid, running from the back of the external pterj'goid plate to the spine of the sphenoid, 

 or the vaginal process of the temporal bone. 



