90 DISSECTION OF THE PTERYGOID REGION. 



from the outer surface of the great wing of the sphenoid bone below the 

 crest, and from the outer surface of the external pterygoid plate. The 

 fibres are directed outwards and somewhat backwards, those attached to 

 the upper margin of the spheno-maxillary fissure forming at first a separate 

 bundle, and are 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 lies on it. By the deep sur- 

 face it is in contact with the inferior maxillary nerve, with a plexus of 

 veins, and with the internal lateral ligament of the joint of the jaw. The 

 parts in contact with the borders of the muscle have been enumerated 

 before. 



Sometimes the slip of the muscle, which is attached to the margin of the 

 spheno-maxillary fissure and the root of the external pterygoid plate, is 

 described as a separate head with an insertion into the interarticular car- 

 tilage. 



Action. If both muscles act the jaw is moved forwards, so that the 

 lower dental arch is placed in front of the upper, and the grinding teeth 

 are rubbed together in an antero-posterior direction. In order that the 

 lower front teeth may be able to pass the others the jaw is depressed. 



One muscle contracting (say the right), the condyle of the same side is 

 drawn inwards and forwards, and the grinding teeth of the lower jaw are 

 moved horizontally to the left across those of the upper. By the alternate 

 action of the two muscles the trituration of the food is effected. 



The INTERNAL PTEKYGOiD MUSCLE (tig. 18, 3 ) is nearly parallel to the 

 ramus of the jaw, and its fibres are longer than those of the preceding 

 muscle. Arising in the pterygoid fossa, and chiefiy from the inner sur- 

 face of the external pterygoid plate, the muscle is further attached below, 

 outside the fossa, to the outer surface of the tuberosity of the palate bone, 

 and to the tuberosity of the upper jaw bone. The fibres descend to be 

 inserted into the angle, and into the inner surface of the ramus of the jaw 

 as high as the inferior dental foramen. 



On the muscle are placed the dental and gustatory nerves, the dental 

 artery, and the internal lateral ligament of the jaw. The deep surface is 

 in relation below with the superior constrictor, and at its origin with the 

 tensor palati muscle. 



Action. From the direction and attachment of the fibres the muscle 

 will unite with the masseter in elevating the jaw. 



Directions. Before proceeding further in the dissection, the student 

 may learn the anatomy of the articulation of the lower jaw. 



TEMPORO-MAXILLARY ARTICULATION. In this articulation are com- 

 bined the condyle of the jaw and the antei-ior part of the glenoid fossa of 

 the temporal bone ; but the osseous surfaces are not in contact, for a piece 

 of fibro-cartilage with two synovial sacs is interposed between them. The 

 bones are retained in apposition mostly by the strong muscles of the lower 

 jaw ; but the following ligaments serve to unite them. 



Capsule. This is a thin fibrous tube inclosing the bones, and is wider 

 above than below. By the upper end it is fixed around the articular 

 surface of the temporal bone in front of the Glaserian fissure ; and it is in- 

 serted below around the condyle of the lower jaw. The space in the 

 interior is divided into two, upper and lower, by a piece of h'bro-cartilago, 

 which is united to the capsule by its circumference. 



The external lateral is a short ligamentous band, being but a part of the 



