FiET. 82. 



138 THE ABTIGULATI0N8. 



with regard to these articulations, as it will be found sufficient to call to mind 

 the topographical description of each piece entering into their formation. 



4. Temporo-maxillary Articulation. 



(Freparation.— Remote the masseter muscle and the parotid gland. Saw through the 

 head about the middle line. Open the articulation externally to exhibit the inter- 

 articular meniscus.) 



The lower jaw, in its union with the cranium, constitutes a double 

 condyloid articulation. 



Articular surfaces. — With the temporal bone, these are the condyle, the 

 glenoid cavity, and the supracondyloid process which exists at the base of 

 the zygomatic process. The glenoid cavity is not lined by cartilage, and 

 appears to be merely covered by synovial membrane. With the maxillary 

 bone there is the oblong condyle situated in front of the coronoid process. 

 Interartieidar fibro-cartilage. — The articular surfaces just named are 

 far from fitting each other accurately ; this is 

 only accomplished by the interposition of a 

 fibro-cartilaginous disc between the temporal 

 and maxillary bones. This disc is a kind of 

 irregular plate, flattened above and below, 

 thicker before than behind, and moulded on 

 each of the diarthrodial surfaces it separates. 

 Its superior face, therefore, presents : in front, 

 a cavity to receive the condyle of the temporal 

 bone ; behind, a boss which is lodged in the 

 glenoid cavity. The inferior face is hollowed 

 by an oblong fossa in which the maxillary con- 

 dyle is lodged. 



Mode of union. — A fibrous envelope — a true 

 capsular ligament — surrounds the articulation, 

 and is attached by its borders to the margin of 

 the articular surfaces it unites. Formed, out- 

 wardly, by a thick fasciculus of white vertical 

 fibres (Fig. 82, 2), this ligament becomes grey- 

 ish-coloured and elastic for the remainder of 

 its extent, and greatly diminishes in thickness, 

 especially iu front. Its inner face is lined by 

 the synovial capsules, and adheres to the cir- 

 cumference of the iuterarticular fibro-cartilage. Its external face responds, 

 in front, to the temporal and masseter muscles ; behind, to the parotid 

 gland ; inwardly, to the external pterygoid muscle ; and outwardly, to a 

 fibrous expansion which separates it from the skin. (Leyh mentions a 

 lateral external and a posterior ligament for this articulation, but Chauveau 

 and Eigot evidently look upon these as portions of the capsular.) 



Synovial membranes. — This articulation has two synovial sacs, one above 

 the other, which are separated by the fibro-cartilaginous disc. 



Movements. — The temporo-maxillary articulation is the centre of all the 

 movements performed by the lower jaw. These are : depression, elevation, 

 lateral motion, and horizontal gliding. 



The lower jaw is depressed when it separates from the superior one, and 

 is elevated when it approaches this. These two opposite movements are 

 executed by a mechanism of such great simplicity that it need not be 



TEMPORO-MAXILLARY AETICU- 

 LATION. 



I, Interarticular fibro-cartilage ; 

 2, External fasciculus of the 

 capsular ligament. — ^A, Base of 

 the coronoid process ; B, Neclt 

 of the maxillary condyle ; C, 

 Mastoid process ; D, External 

 auditory hiatus. 



