136 TOPOGRAPHICAL ANATOMY OF THE 



M. PTERYGOIDEUS INTERNUS, — The internal pterygoid ^ muscle is 

 large and strong, being possessed of a considerable admixture of 

 tendinous tissue. Arising from the rough ridge formed by the pterygoid 

 process of the sphenoid and the neighbouring part of the palatine bone, 

 it spreads out in a fan-like manner and is inserted into the medial 

 surface of the mandible. 



Dissection. — The internal pterygoid nuiscle should be removed in order 

 that the external muscle of the same name may be examined. 



M. PTERYGOIDEUS EXTERNUS. — The external pterygoid, much 

 smaller than the internal muscle of that name, takes origin from the 

 pterygoid process of the sphenoid bone and is inserted into the 

 mandible close to its condyloid process. 



Dissection. — Remove all the muscles, &c., from about the joint 

 between the mandible and the temporal bone on that side of the head 

 upon which the articulation is still intact. 



The mandibular articulation (Articulatio mandibularis). — The 

 mandibular joint occurs between the condyloid process of the mandible 

 and the articular tuber, mandibular fossa and postglenoid process of the 

 temporal bone. When the joint is at rest, the condyloid process of the 

 mandible lies in the mandibular fossa of the temporal ; but when the 

 mouth is opened, it glides forwards on to the articular tuber and carries 

 the articular disc with it. 



The component bony surfaces of the joint are not in actual contact, 

 for between them there is an articular disc (discus articularis) of fibro- 

 cartilage, the upper surface of which is convex to fit the mandibular 

 fossa, while its lower surface is concave for adaptation to the mandibular 

 condyloid process. The joint is enclosed by a caijside attached around 

 the articular surfaces of the two bones and also to the circumference 

 of the articular disc. Thus it comes to pass that there are two joint 

 cavities ; one between the temporal bone and the articular disc ; the 

 other, less roomy, between the disc and the condyloid process of the 

 mandible. In general, the capsule is strong, but the presence of a 

 tempoi'o - mandibular ligament (ligamentum temporomandibulare) 

 makes it especially so laterally. A 'posterior ligament (ligamentum 

 posticum), composed of elastic fibres, runs from the post-glenoid process 

 of the temporal bone to the posterior border of the mandible just 

 below the condyloid process. 



Naturally, the freest movements in the mandibular joint are such as 

 result in depression and elevation of the mandible. In addition, how- 



^ nrepv^ (pteryx) [Gr.], a wing (referring to the origin of the nmscle from the 

 pterygoid process of the sphenoid). 



