Royal Physical Society. 377 



"'Professor Owen has directed attention to the fact, that with 

 three exceptions (Echidna, Ornithorhynchus, and Tarsipes), all 

 the species of marsupials had the angle of the lower jaw bent 

 inwards, encroaching on the space between the two branches. 

 That on looking down upon the margin of the jaw a more or 

 less flattened surface is observed, extending between the ex- 

 ternal ridge and internal inflected angle. This character is 

 strikingly manifested in the wombat. Instead of the usual 

 vertical compressed form of this portion of the lower jaw, a 

 strongly depressed horizontal form is observed, with deep hol- 

 low spaces for the insertion of the masseter muscles externally, 

 and the internal pterygoids within, two muscles which, along 

 with the external pterygoids inserted into the sigmoid notch 

 before the condyles, and the temporal muscles surrounding the 

 coronoid process, are those chiefly concerned with the move- 

 ment of the jaws in the act of mastication. A large foramen 

 is seen at the outside of the posterior mental foramina, probably 

 for the transmission of nerves from the inferior maxillary 

 branch of the fifth pair, to the largely developed masseters ; 

 which usually pass, along with the blood-vessels, over the' sig- 

 moid notch." The characters afforded by the teeth were next 

 briefly described : — " Two nearly straight incisors, three inches 

 in length, occupy the narrow extremity of the lower jaw, ex- 

 tending directly backwards a little beyond the bifurcation; 

 and two, deeply implanted in the premaxillaries, much curved 

 and twisted, occupy the upper jaw. 



" One single and four double molars, with flat triangular 

 crowns deeply inserted in the alveoli, complete the dental for- 

 mula. There is a marked difference in the position of the 

 molars in the two jaws ; whereas the curvature of the molar 

 teeth in the lower jaw have their convexity turned outwards, 

 it is exactly the reverse in the upper, so that when the jaws 

 are closed the external triangular apex of the teeth in the 

 lower jaw meet the broader external base of those in the upper. 

 The teeth have no roots, and they are all more or less hollow 

 at the base. 



" From an examination of the figures in the second volume of 

 the work of Sir Thomas L. Mitchell, and comparing Professor 

 Owen's description of the prismatic form of the teeth with those 



