78 COMPAKATIVE DENTAL ANATOMY 



Evolution of the Temporo-mandibular Articu- 

 lation. With the evolution of the tooth forms 

 and the occlusion of the teeth we notice a cor- 

 responding change in the jaw forms and the 

 temporo-mandibular articulation. In those ani- 

 mals which have occlusion of tooth-bearing sur- 

 faces, the temporo-mandibular articulation is very 

 loosely constructed and the condyle and glenoid 

 fossa have very little shape. In those animals 

 which have occlusion of rows of teeth, there is 

 more of a condyle and glenoid fossa. In the alli- 

 gators, owing to the anatomical structure of the 

 animal, we find that the condyle is concave and 

 the glenoid fossa convex and the mandible is the 

 more stationary bone when the mouth is opened. 

 In those animals with occlusion of the cusps, we 

 find the articulation influenced by the shape of the 

 cusp. In the animals which have long cusps, 

 the glenoid fossa is decidedly concave, and in 

 those in which the cusp is short the glenoid fossa 

 is only slightly concave and often entirely flat. 

 When we find the cusps of the teeth so arranged 

 that the tooth has a long antero-posterior diam- 

 eter the condyle has a great bucco-lingual diam- 

 eter. The greatest diameter of the tooth is 

 always the opposite to the greatest diameter of 

 the condyle. In man, we find that the shape 

 of the condyle changes as the occlusion changes. 

 In fact, in young animals of whatever family, the 



