312 



THE AETICULATIONS OE JOINTS. 



Tubevculum articulare 



MANDIBLE 



FIG. 299. SECTION THROUGH THE MANDIBULAB 

 JOINT. 



ARTICULATIO MANDIBULARIS. 



The mandibular joint (O.T. temporo-mandibular) is an arthrodial diarthrosis. It 

 occurs between the mandibular fossa of the temporal bone and the condyle of 

 the mandible. These two articular surfaces are markedly dissimilar both in size 

 and shape. In its general outline the articular surface of the head of the 



mandible is cylindrical, having its long 

 axis directed from the medial side laterally 

 and forwards. On the other hand, the 

 mandibular fossa is concavo-convex from 

 behind forwards. Its articular surface 

 includes the tuberculum articulare the 

 eminence at the base of the anterior root 

 of the zygoma. The articular surfaces of 

 the bones are clothed with hyaline en- 

 crusting cartilage, whilst the articular 

 cavity is divided into a superior and 

 inferior part by a disc of fibro-cartilage. 



Ligaments. The joint is invested by 

 an articular capsule which is quite com- 

 plete, but is very thin on the medial side. 

 The lateral part of the fibrous stratum of 

 the capsule the temporo-mandibular liga- 

 ment (O.T. external lateral) (Fig. 298) is divisible into anterior and posterior 

 portions which are attached superiorly to the root tubercle and inferior border 

 of the zygoma tic process of the temporal bone, and inferiorly to the lateral side 

 and posterior border of the neck of the mandible. The direction of its fibres is 

 downwards and backwards. 



Within the capsule there is a disc of fibro-cartilage, the discus articularis 

 (Fig. 299), which is moulded upon the condyle of the mandible below, and on the 

 articular surface of the temporal bone above. It thus compensates for the 

 incongruity between the articular 

 surfaces of the two bones. The disc 

 is attached circumferentially to the 

 capsule. It is widest in the trans- 

 verse direction, thicker posteriorly 

 than anteriorly, and thinnest towards 

 the centre, where it may be perforated. 

 Its anterior margin is intimately 

 associated with the insertion of the 

 external pterygoid muscle. 



A synovial stratum lines each of 

 the compartments into which the 

 joint cavity is divided by the disc. 

 As a rule these membranes are 

 separate from each other, but they 

 become continuous when the disc 

 is perforated. The superior synovial 

 stratum is larger and more loosely 

 disposed than the lower. 



Situated on the medial aspect of the joint, but at a short distance from it, and 

 quite distinct from the capsule, there is an accessory band called the lig. spheno- 

 mandibulare (Fig. 300). Superiorly the spheno-mandibular ligament (O.T. internal 

 lateral) is attached to the angular spine of the sphenoid bone, and inferiorly to 

 the inferior as well as the anterior border or lingula of the inferior alveolar 

 foramen. It is not an articular ligament in the true sense ; for, instead of being 

 connected with the joint, it is developed in the tissue surrounding part of Meckel's 

 cartilage. 



Spheno-mandibular 

 ligament 



Styloid process 



Stylo-mandibular 

 ligament 



FIG. 300. SPHENO-MANDIBULAR LIGAMENT OF THE 

 MANDIBULAR JOINT. 



