610 



DISSECTION OF THE PTERYGOID REGION. 



Nerves. 



External 

 pterygoid 



origin ; 



insertion, 



relations ; 



use of both 

 muscles, 



of one 

 muscle. 



Internal 

 pterygoid : 



origin ; 



insertion ; 



contiguous 

 parts ; 



upwards and downwards : sometimes the artery is placed beneath 

 the muscle as in fig. 218. The veins, which form a large plexus 

 between the muscles, may be taken away. 



Position of nerves. Most of the branches of the inferior maxillary 

 nerve are seen in this dissection, (fig. 219 and fig. 222, p. 616). 

 Thus, the masseteric and posterior and middle deep temporal nerves 

 appear between the upper border of the external pterygoid and the 

 skull, while the buccal nerve, with the anterior deep temporal nerve, 

 passes through the fore part of the muscle between its two heads. 

 Issuing from beneath the lower border of the muscle are the large 

 inferior dental and lingual nerves, the latter being the anterior of 

 the two ; and coming out behind the condyle of the jaw is the 

 auriculo-temporal nerve. The small posterior dental branch of the 

 superior maxillary nerve is also to be found, lying with the artery 

 of the same name on the hinder part of the upper jaw. 



The EXTERNAL PTERYGOID MUSCLE (fig. 218, 2 ) is triangular in 

 shape, and arises by two heads, which are separated by an interval 

 opposite the spheno-maxillary fossa. The upper head is the smaller, 

 and is attached to the fore part of the zygomatic surface of the 

 great wing of the sphenoid bone ; the lower head springs from the 

 outer surface of the external pterygoid plate. From this origin the 

 muscle runs backwards and outwards to be inserted into the hollow 

 in front of the neck of the lower jaw-bone, and into the interarticular 

 fibro-cartilage of the joint. 



Externally the pterygoid is concealed by the temporal muscle 

 and the lower jaw ; and the internal maxillary artery usually lies 

 on it. Its deep surface is in contact with the internal pterygoid, 

 the inferior maxillary nerve and its branches, and the internal lateral 

 ligament of the jaw. Through the interval between the heads pass 

 the buccal and anterior deep temporal nerves in a common stem 

 and the internal maxillary artery, when the latter is placed beneath 

 the muscle. The parts in contact with the borders of the external 

 pterygoid have been enumerated above. 



Action. If both muscles contract, the jaw is moved directly 

 forwards, so that the lower dental arch is placed in front of the 

 upper ; but if one muscle act alone (say the right), the condyle of 

 the same side is drawn forwards, and the grinding teeth of the 

 lower jaw are moved obliquely to the left across those of the upper. 

 By the alternate action of the two muscles the trituration of the 

 food is mainly effected. 



The INTERNAL PTERYGOID MUSCLE (fig. 218, 3 ) crosses the direc- 

 tion of the external, and is nearly parallel to the ramus of the jaw. 

 It arises in the pterygoid fossa, mainly from the inner surface of 

 the external pterygoid plate, and by a small slip from the outer 

 surface of the tuberosity of the palate bone and the superior maxilla 

 in front of the pterygoid process. The fibres descend to be inserted 

 into a rough mark on the inner side of the ramus of the lower jaw, 

 extending from the inferior dental foramen to the angle. 



On the muscle are placed the inferior dental and lingual nerves, the 

 inferior dental vessels, and the internal lateral ligament of the jaw. 



