180 THE ARTICULATIONS 



(1) THE TEMPORO-MANDIBULAR ARTICULATION 



Class. — Diarthrosis. Subdivision. — Condi/larthrosis. 



The parts entering into tlie formation of this joint are: — the anterior i)ortion of 

 tlie glenoid fossa and glenoid ridge (eniinentia articularis) of the temporal l)(>ne 

 above, and the eondyle of the lower jaw below. Both are covered with articular 

 cartilage, which extends over the front of the glenoid ridge to facilitate the play of 

 the interarticular cartilage. The ligaments Avhich unite the bones are : — 



1. Capsular. 3. Spheno-mandibular. 



2. Interarticular filiro-cartilage. 4. Stylo-mandibular. 



The capsular ligament is often described as consisting of four j^ortions, which 

 are, however, continuous with one another around the articulation. 



1. The anterior portion consists of a few stray fibres connected with the 

 anterior margin of the tibro-cartilage, and attached below to the anterior edge of 

 the condyle, and alcove to the front of the glenoid ridge. Some fibres of insertion 

 of the external pterygoid pass between them to be inserted into the margin of the 

 fibro-cartilage. 



2. The posterior portion is attached above, just in front of the Glaserian 

 fissure, and is inserted into the Ijack of the jaw just below its neck. 



3. The external portion or external lateral ligament (fig. 191) is the 

 strongest part of the capsule. It is broader aljove, where it is attached to the 

 lower edge of the zygoma in nearly its wdiole length, as well as to the tubercle at 

 the point where the two roots of the zygoma meet. It is inclined doAvnw'ards and 

 l)ackwards, to l)e inserted into the outer side of the neck of the condyle. Its fibres 

 diminish in obliquity and strength from before backwards, those coming from the 

 tubercle being short and nearly vertical. 



4. The internal portion or short internal lateral ligament (fig. 192) consists 

 of well-defined fibres, having a broad attachment, above to the outer side of the alar 

 spine of the sphenoid and inner edge of the glenoid fossa; and below, a narrow 

 insertion to the inner side of the neck of the condyle. Fatty and cellular tissue 

 separate it from the spheno-mandibular ligament which is internal to it. 



The interarticular cartilage (fig. 193) is an oval plate interposed between and 

 adapted to the two articular surfaces. It is thinner at the centre than at the 

 circumference, and is thicker behind where it covers the thin bone at the bottom 

 of the glenoid fossa wdiich separates it from the dura mater, than in front where it 

 covers the glenoid ridge. Its inferior surface is concave and fits on to the condyle 

 of the lower jaw; while its superior surface is concavo-convex from before back- 

 wards, and is in contact with the articular surface of the temporal bone. It 

 divides the joint into two separate synovial cavities, but is occasionally perforated in 

 the centre, and thus allows tliem to communicate. It is connected with the cap- 

 sular ligament at its circumference, and has some fibres of the external pterygoid 

 muscle inserted into its antericir margin. 



There are usually two synovial membranes (fig. 193), the superior being the 

 larger and looser, i)assing down from the margin of the articular surface above, to 

 the upper surface of the interarticular cartilage below; the lower and smaller one 

 passes from the interarticular cartilage above to the eondyle of the jaAV below, 

 extending somewhat further down behind than in front. When the interarticular 

 cartilage is perforated, the two sacs communicate. 



The spheno-mandibular ligament (long internal lateral) (fig. 192) is a thin, 

 loose band, situated some little distance from the joint. It is attached above to 

 the alar spine of tlie s])henoid and contiguous part of the temporal l)one, and is 

 inserted into the mandil)ular spine of the lower jaw. It covers the upper end of 

 the mylo-hyoid groove, and is here ])ierced l)y the viylo-hyoid nerve. Its origin is 

 a little internal to, and immediately behind, the origin of the short internal lateral 

 ligament. It is separated from the joint and ramus of the jaw by the external 

 pterygoid muscle, intcnud maxillary artery and vein, the mandihular nerve and 



