LIGAMENTS OF THE LOWER JAW. 



Ill 



Fig. 47 * 



Fig. 48.t 



tion. These fibres scarcely deserve consideration as a distinct 

 ligament. 



The interarticular fibro-cartilage is a thin oval plate, thicker at 

 the edges than in the centre, and placed horizontally between the 

 head of the condyle of the 

 lower jaw and the glenoid ca- 

 vity. It is connected by its 

 outer border with the external 

 lateral ligament, and in front 

 receives some fibres of inser- 

 tion of the external pterygoid 

 muscle. Occasionally it is in- 

 complete in the centime. It 

 divides the joint into two dis- 

 tinct cavities, the one being 

 above and the other below the 

 cartilage. 



The synqvial membranes are situated the one above, the other 

 below the fibro-cartilage, the former being the larger of the two. 

 When the fibro-cartilage is perforate, the synovial membranes com- 

 municate with each other. 



Besides the lower jaw, there are 

 several other joints provided with a 

 complete interarticular fibro-cartilage, 

 and consequently, with two synovial 

 membranes; they are, the sterno-clavi- 

 cular articulation, the acromio-clavi- 

 cular, and the articulation of the ulna 

 with the cuneiform bone. 



The interarticular fibro-cartilages 

 of the knee-joint are partial, and 

 there is but one synovial membrane. 



The articulations of the heads of the 

 ribs with the vertebra? have two syno- 

 vial membranes, separated by an interarticular ligament without 

 fibro-cartilage. 



Actions. The movements of the lower jaw are depression by 



* An internal view of the articulation of the lower jaw. 1. A section through the 

 petrous portion of the temporal bone and spinous process of the sphenoid. 2. An 

 internal view of the ramus, and part of the body of the lower jaw. 3. The internal 

 portion of the capsular ligament. 4. The internal lateral ligament. 5. A small interval 

 at its insertion through which the mylo-hyoidean nerve passes. 6. The stylo-maxillary 

 ligament, a process of the deep cervical fascia. 



t In this sketch a section, has been carried through the joint, in order to show the 

 natural position of the interarticular fibro-cartilage, and the manner in which it is 

 adapted to the difference of form of the articulating surfaces. 1. The glenoid fossa. 

 2. The eminentia articularis. 3. The interarticular fibro-cartilage. 4. The superior 

 synovial cavity. 5. The inferior synovial cavity. 6. An interarticular fibro-cartilage, 

 removed from the joint, in order to show its oval and concave form; it is seen from 

 below. 



