511 



liüder, considerably enlarged posteriorly to form the malleus, and 

 bearing behind a twisted articular face for the reception of the incus. 

 The malleo-meckelian bar carries a membrane bone below, and the 

 tympanic lies ventral to, and rather to the outside of, Meckel. 



These bones and cartilages lie freely in the hollow of the dentary, 

 which is a very thin ossification, gently concave outwards above, 

 and more strongly concave below where it curves round Meckel. 

 The corono-condylar notch is very deep, so that the coronoid extends 

 back nearly as far as the condylar process. 



Pig. 1. External view of posterior part of lower jaw in foetal Perameles. 

 dent, dentary ; in. incus ; ml. body of malleus ; mn. manubrium of the malleus ; 

 s.ang. surangular (?) ; st. stapes ; ty. tympanic. 



In the condylar region there is a certain amount of imperfectly 

 formed cartilage. That cartilage occurs in this region is well known, 

 but in Perameles the tissue is always peculiar and never of a distinct 

 hyaline nature. This fact, together with the greater abundance of 

 this tissue in later stages, weighs against Fuch's view that the mass 

 represents the Eeptilian articular. Further, this region of the dentary 

 is not the only part of the bone that ossifies from cartilage, for 

 in this foetus the anterior part of the bone develops in the same 



