254 TEETH OF DICYNODON. 



The direction of the tusks is forwards, downwards, and 

 very slightly inwards ; the two converging in the descent 



Fig. 64. 



SKULL AND TUSKS OF Dicynodon lacerticcjj/,: 



along the outer side of the compressed symphysis of the 

 lower jaw, cc. The tusk is principally composed of a 

 body of compact unvascular dentine. The base is exca- 

 vated by a wide conical pulp-cavity, p, with the apex 

 extending to about one-half of the implanted part of the 

 tusk, and a linear continuation extending aloDg the centre 

 of the solid part of the tusk. 



Until the discovery of the rhynchosaurus, this edentu- 

 lous and horn-sheathed condition of the jaws was supposed 

 to be peculiar to the chelonian order among reptiles ; and 

 it is not one of the least interesting features of the dicy- 

 nodonts of the African sandstones, that they should repeat 

 a chelonian character hitherto peculiar. amongst lacertians, 

 to the above-cited remarkable extinct edentulous genus 

 of the new red sandstone of Shropshire; but our interest 

 rises almost to astonishment when, in a saurian skull, we 

 find, superadded to the horn-clad mandibles of the tor- 

 toise, a pair of tusks, borrowed, as it were, from the mam- 

 malian class, or rather foreshadowing a structure which. 



