1906.] 



ARTICULATION OF THE VERTEBRATE JAW. 



117 



is greater between the teeth which are furthest back, near the 

 points A and B, than between the front ones, near the points D 

 and E. But though the pressure at right angles to the level 

 edges of the jaws is not equal in all parts, the oblique forward 

 pressure of the lower jaw on the upper as it slides up underneath 

 it is more nearly equal in proportion as the angle E A C 

 approaches a light angle. The molar teeth of the Hare may be 

 seen to have their flat biting-surfaces set obliquely : those of the 

 upper jaw look dow^nwards and backwards ; those of the lower jaw 

 look forwards and upwards. The plane in which they meet 

 simultaneously is at right angles to the line of force (text-fig. 39). 



Text-fig. 39. 



Diagram of jaws. Type 2. 



Showing the crowns of the teeth set in a plane at right angles to the 

 greatest pressure. 



Text-fig. 40. 



Diagram of jaws. Type 2. Showing the emeneutia articularis. 



Further, economy of movement is obtained in this type by the 

 condyle of the jaw not only rotating, but also gliding forward on 

 to the eminentia articularis. By this means the point A, at the 

 same time that it is separated from B, is depressed, and thus so 

 wide a gape is not necessitated, and also the parallelism of the 

 teeth, and possibly also the position of the inferior dental foramen, 

 is not so much disturbed (text-fig. 40). The molars are also 

 lequired to make to-and-fro movements over one another. They 



