2io EDENTATA 



having a rudimentary crown, and a distinct anterior and posterior 

 root. The other milk-teeth are styliform, the four anterior ones 

 being very minute, and separated from one another by equal 

 intervals ; the foremost of all is situated immediately behind the 

 premaxillo-maxillary suture. In the mandible only four milk-teeth 

 have hitherto been detected, of which the hindmost has the 

 comparatively complex form found in the corresponding upper tooth. 

 None of these milk-teeth appear, however, to cut the gum, so that 

 the whole set is entirely functionless. Under the microscope these 

 milk-teeth show signs of possessing a commencement of the 

 remarkable histological structure found in the permanent teeth. 



Mr. Thomas remarks that since " the three large posterior teeth 

 of Oryderopus, already distinguished by their more molariform shape, 

 do not have milk-predecessors, while all the small teeth anterior to 

 them do, and in addition the last milk-tooth is markedly different 

 from those in front of it, we ought apparently no longer to look 

 upon this animal as an homodont, but instead to consider it as an 

 originally heterodont form in Avhich the incisors and canines have 

 been suppressed to allow free play to the mobile vermiform tongue. 



"But important as a knowledge of the presence of a milk- 

 dentition in Oryderopus is, it does not at present render any easier 

 the difficult cpiestions as to the phylogeny and systematic position 

 of that animal. Although called an Edentate, it has always been 

 recognised as possessing many characters exceedingly different from 

 those of the typical American members of the order. It has in fact 

 been placed with them rather on account of the inconvenience of 

 forming a special order for its reception than because of its real 

 relationship to them. Now, as they are either altogether toothless, 

 or else homodont and monophyodont (apart from the remarkable 

 exception of Tatusia), it seems more than ever incorrect to unite 

 with them the solitary member of the Tubulidentata, toothed, 

 heterodont, and diphyodont, and differing from them in addition by 

 its placentation, the anatomy of its reproductive organs, the minute 

 structure of its teeth, and the general characters of its skeleton. 



"But if Oryderopus is not genetically a near relation of the 

 Edentates, Ave are wholly in the dark as to what other mammals it 

 is allied to, and I think it would be premature to hazard a guess on 

 the subject. "Whether even it has any special connection with 

 Manis is a point about which there is the greatest doubt, and unfor- 

 tunately we are as yet absolutely without any paleeontological 

 knowledge of the extinct allies of either. Macrotherivm even, 

 usually supposed from the structure of its phalangeal bones, to be 

 related to Manis, has lately proved to have the teeth and vertebra? 

 of a perissodactyle Ungulate, and one could not dare to suggest 

 that ancestors of Manis, or Oryderopus were to be sought in that 

 direction. Lastly, as the numerous fossil American Edentates do 



