336 Mr Owen ow the Dicynodon. 



the Dicynodon to Crocodilians and Chelonians are much more 

 strongly manifested than they are in the Rhynchdsaurus. 



The author, in concluding his account of the Dicynodon, ad- 

 verts to the analogy of structure, which radiates from this 

 genus in the direction of the Ophidian division of existing 

 Reptilia, although it is unsupported by any other concordances 

 of cranial or dental organisation than those about to be cited. 

 In the poisonous serpents, the rattle-snakes for example, the 

 intermaxillary bone is single and edentulous ; the maxillary 

 bone supports a long, curved, pointed tooth, which, when ad- 

 vanced, descends outside the lower jaw. Apart from all the 

 other peculiarities of the maxillary, and dental systems of the 

 poison-snakes, they alone, of all existing Reptllia, repeat, in 

 the above-cited structures, the characters of the Dicynodon. 

 But, in addition to the two large maxillary teeth, the rattle- 

 snake has smaller teeth in rows upcm the palatine, pterygoid 

 and mandibular bones. To complete the resemblance between 

 the tusks of the Dicynodon and the venom fangs of the snake, 

 you must deeply groove their fore-part, or bore a canal through 

 their centre ; you must remove those strong columns of bone 

 which converge to, abut against, and strengthen the fixed 

 socket of the tusk, and you must suspend the maxillary bone 

 by a moveable pedicle to the prefrontal and malar bones. 

 Besides, the perforated tusk of the poisonous serpent is always 

 followed by one oi* more similar teeth, in various stages of 

 growth, ready to supply its place, according to the general law 

 of the maintenance in serviceable state of the dental armature 

 of the jaws throughout the Reptilian class. 



The canine tusk of the Dicynodon consists of a simple body 

 of compact unvascular dentine, with a very thin outer coat of 

 enamel, which may be traced into the alveolus for a short dis- 

 tance. Rather more than one-third of the tusk is lodged in 

 the socket, the basal conical pulp-cavity is continued from the 

 base about one half down the implanted part of the tusk, and 

 a linear continuation extends along the centre of the rest of 

 the tusk, from which the dentinal tubes of the solid body of 

 the tusk radiate. They present gentle parallel secondary curves 

 or undulations throughout their course, divide dichotomously 



