I2l6 



A MANUAL OF ANATOMY 



insertion to the external pterygoid muscle. It divides the joint into 

 two compartments, upper and lower, which are usually distinct. 



The synovial membranes are two in number, upper and lower, 

 one being above and the other below the plate of fibro-cartilage. 

 The upper synovial membrane is larger and looser than the lower, 

 and, when the plate of fiibro-cartilage is perforated at the centre, 

 the two synovial membranes are continuous through the perforation. 



Arterial Supply. — ^The superficial temporal artery chiefly. 



Nerve-supply. — ^The auriculo- temporal nerve and offsets from the 

 masseteric nerve. 



Movements. — These are as follows : (i) depression, (2) elevation, (3) pro- 

 traction, (4) retraction, and (5) lateral movements. There being two divisions 

 of the joint, upper and lower, different movements occur in each. The move- 

 ment in the upper compartment is of a gliding character, whilst in the lower 

 compartment it is of a ginglymoid or hinge character. When the mandible 

 is depressed, as in opening the mouth, the condyle and the plate of fibro- 

 cartilage move forwards on to the eminentia articularis. In cases of over- 

 depression, as in violent yawning, or forcing too large a body into the mouth, 

 the condyle is apt to slip over the eminentia articularis into the zygomatic 

 fossa, and, when this takes place, dislocation of the mandible is the result. 



Meatus Auditorius 

 Externus 



Condyle (in section)i 



Coronold Process 



Mastoid Process 



Styloid Process 



Fig. 498. — The Temporo-Mandibular Joint Opened (External View). 



The movement of forward gliding on the part of the condyle and plate of 

 fibro-cartilage during depression takes place in the upper compartment "of 

 the joint. Another movement, however, of a ginglymoid or hinge character 

 is taking place in the lower compartment of the joint, namely, between the 

 condyle and the interarticular plate. This consists in the condyle rotating 

 on the under surface of the plate round a transverse axis. 



When the mandible is elevated, as in shutting the mouth, the changes which 

 occur in both compartments of the joint are the reverse of those just described 

 as taking place in depression. The condyle and fibro-cartilage glide backwards 

 into the glenoid cavity, and at the same time the condyle rotates back to its 

 previous position. In protraction, as when the lower incisors are protruded 

 beyond the upper, and in retraction, the movement mainly takes place in the 

 upper compartment of the joint, and consists in the condyle and plate of fibro- 

 cartilage gliding forwards and backwards. When these movements are per- 



