154 



Having now summed up as much of my series of observations with 

 regard to the Artiodactyle division as I think it at present expedient 

 to offer, I proceed to consider the Perissodactyle group. 1 observe 

 that Prof. Owen separates the Proboscidia as a third group, to which 

 he seems to assign a rank equivalent to that of the other two, and 

 passes the Deinotheriiim and the Toxodon, as well as the " Sirenoid " 

 forms, with some remarks which do not assign to them any very defi- 

 nite location. There will always be room for difference of o{)iuion as 

 to the rank that should be assigned to a group, even when its limits 

 are fully recognised ; since, as I have elsewhere endeavoured to show *, 

 " granting affinities and even groups to be natural, the limits assigned 

 to those degrees of difference and similarity which we are wont to in- 

 dicate by definite ierms are not ;" but it seems to me, that although 

 these more aberrant groups of Ungulata possess several peculiarities 

 which are entirely their own, they do not diifer from the Perisso- 

 dactyla in essential characters to the same degree as the latter do 

 from the Artiodactyla, while in certain respects they agree among 

 themselves, as though they would constitute a second subdivision of 

 the Perissodactyla again divisible into strongly marked families. 

 Among the characters which I have brought forward, we find that 

 the Proboscidia, the Sirenia, and the singular fossil genus Toxodon, 

 agree with the more typical Perissodactyla in the depth of the inter- 

 maxillary bone and the vertical implantation of the incisors, in the 

 absence of the supraorbital foramen, of the fossa and pit within the 

 orbit, and of a strongly marked pterygoid ridge, in the character of 

 the zygoma, except that in the Proboscidia there is no descending 

 post-articular process ; in the narrowing anteriorly, and rounded sides 

 of the basioccipital bone, and in the resemblance between the anterior 

 and posterior molares. They differ from the typical Perissodactyla 

 and agree among themselves, in the upward direction of the nasal 

 opening, the large size of the infraorbital foramen, the lengthening 

 of the bony palate, with the comparative narrowing of the posterior 

 nares, in the short antero-posterior extent and the transverse thicken- 

 ing of the pterygoid processes, and in the considerable angle formed 

 between the basioccipital and basisphenoid bones (least marked in 

 the Manatee), the latter being inchned upwards, of course with refer- 

 ence to the upward direction of the nasal canal. Points of resem- 



to the upper molars of the Dichodon seems to have crossed the mind of Prof. 

 De Blainville, for in a recent number of the ' Ostuographie,' after describing the 

 dentition of the lower jaw in that animal, he proceeds : " D'apres ce qui vient 

 d'etre dit du systeme dentaire de cette mandibule, on voit qu'il est incomplet par 

 I'absence de la derniere molaire non encore sortie ; mais ne doit-il pas en etre de 

 meme pour la serie d'en haut, si les deux pieces proviennent du meme individu? 

 Alors il faudrait admettre qu'au lieu de deux, il ne manquerait qu'une seule avant- 

 molaire, ce qui parait peu probable." 



With regard to the Hyopotamiis Vectianus, M. De Blainville seems to doubt a 

 little that the upper and lower jaw really belong to each other, but refrains from 

 a decided judgement, not yet being acquainted, as he observes, with any principle 

 that can direct the mind in the question of the relation of two parts of the dental 

 system to each other. He inadvertently calls this species " annectens," the name 

 given by Prof. Owen to his Paloplotherium. 



* Essay on Classification, ' Zoologist ' for December 1847. 



