Prof. Owen on the genus Dicynodon. 79 



linking the Dicynodon to Crocodilians and Chelonians are much more strongly 

 manifested than they are in the Rhynchosaurus. 



Before concluding this summary, I cannot omit adverting to an analogy of 

 structure which radiates from the Dicynodon in the direction of the Ophidian 

 division of existing Reptiles, although it is unsupported by any other concordances 

 of cranial or dental organization than those which I am about to cite. In the 

 poisonous Serpents, the Rattle-snake, for example, the intermaxillary bone is 

 single and edentulous ; the maxillary bone supports a long, curved, pointed tooth, 

 which, when advanced, 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 Reptiles, 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 upon the palatine, pterygoid and mandibular bones. To com- 

 plete 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 pre-frontal and malar bones. Besides, 

 the perforated tusk of the poisonous Serpent is always followed by one or 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. 



I have made various sections in fragmentary specimens, and have closely in- 

 spected every example of the Dicynodon where the alveoli of the tusks were ex- 

 posed, in quest of the germs of successional teeth or tusks of reserve, but without 

 success. From the youngest specimen with tusks of two lines diameter, to the 

 largest with tusks of two inches diameter, in which their inserted part is exposed 

 to the base, they alike exhibit a conical excavation of that base* for the lodgement 

 of a persistent matrix, and are solid in the remainder of their extent. In con- 

 sequence of the peculiarly complex structure discovered in the tusks and teeth of 

 the Labyrinthodonts of the new red sandstone, I was very desirous, from the com- 

 mencement of the present investigation, to submit the tissue of the great canines 

 of the Dicynodons to microscopic examination, and, with the sanction of the Pre- 

 sident, I have had the requisite longitudinal and transverse sections prepared from 

 fragmentary portions of skulls containing portions of these teeth. 



They offer no trace of the inflected labyrinthic folds of the capsule to which the cha- 

 racteristic ichthyic interblending of the cement and dentine in the teeth of the great 

 Keuper Batrachian is due, but the microscopic specimens give additional evidence 



* PI. V. fig. 3, d. 



M 2 



