THE MOVEMENTS OF THE LOWER JAW. 613 



the temporal bone, and is larger than that on the jaw. It includes 

 the deep oval hollow formed by the part of the glenoid fossa 

 in front of the Glaserian fissure, and the convex surface, known as 

 the articular eminence, which forms the anterior boundary of the 

 hollow. 



Movements of the joint. The lower jaw has up and down, forward Kinds of 

 and backward, and oblique movements. 



In depressing the jaw. as in opening the mouth, the condyle I" opening 



* i J.MI / i j 1 f^ * i the mouth 



moves forwards till it is placed under the convexity of the articular how condyle 

 eminence ; but the interposed concave fibro-cartilage gives security moves - 

 to the joint. Even with this provision, a slight degree more of 

 sudden motion may throw the condyle off the prominence of the 

 temporal bone into the zygomatic fossa, and give rise to dis- Dislocation, 

 location. 



In this movement the fore and lateral parts of the capsule are state of 

 tightened ; and the nbro-cartilage is drawn forwards with the 1J 

 condyle by the external pterygoid muscle. 



When the jaw is elevated and the mouth closed, the condyle and Shutting 

 the fibro cartilage glide back into the glenoid fossa; and the 

 posterior part of the capsule is stretched. 



During the horizontal movements forwards and backwards of the Forward and 

 jaw the condyle is placed successively opposite the front and back movement. 

 of the temporal articular surface ; and the nbro-cartilage always 

 follows the condyle of the jaw, even in dislocation. 



Excessive motion forwards would be prevented by the coronoid 

 process of the jaw striking against the zygomatic arch ; and the 

 backward movement is checked by the external lateral ligament 

 and by the meeting of the condyle with the postglenoid process of 

 the temporal bone. 



The oblique movement is produced by the condyle of one side Oblique 

 advancing on the articular eminence, while the other remains in how 6 ^' 

 the glenoid fossa. If the right condyle advances, the chin moves produced, 

 to the left side, and the grinding teeth of the lower jaw are carried 

 obliquely to the left and forwards across the upper set. By the 

 alternate action to opposite sides the food is triturated. 



Dissection. The condyle of the jaw is next to be disarticulated JJl^ 11 - " 

 and drawn forwards with the attached external pterygoid muscle, maxillary 

 so as to allow the inferior maxillary nerve to be seen (fig. 222, ljerve > 

 p. 616). While cutting through the joint-capsule, the dissector 

 must be careful of the auriculo- temporal nerve close beneath. 



On turning forwards the pterygoid muscle, and removing some its trunk - 

 fat and veins, the dissector will find the trunk of the inferior 

 maxillary nerve. The masseteric, temporal, and buccal branches JJj h . 

 of the nerve should be traced to a common origin close below the 

 foramen ovale of the sphenoid bone. The dental and lingual 

 nerves should be cleaned beneath the muscle ; and the auriculo- 

 temporal nerve followed forwards with care from the back of 

 the articulation to its origin from the trunk. The small chorda {^ m h r n c j a 

 tympani is to be found joining the back of the lingual nerve near 

 tlie skull. 



