

AFFINITIES OF RODENTS. 



serially homologous fact is presented to us in the possession by the American 

 Pliocene Mastodons of a band of enamel on their tusks (see Marsh, /. c. p. 41). 



The naked-eye structure of the molars of many Rodents, such as the Capybara, 

 is strikingly like that of the Elephants, and the microscopic arrangement of the 

 enamel in the same teeth in the Elephant and the Mastodon has been shown to 

 be of the same type as that observable in all Rodents except the Leporidae and 

 the Hystricidae. The coronoid processes of the lower jaw are small, and the 

 relations of the malars to the malar processes of the maxillaries and of the squamous 

 bones are the same in both orders, both the latter bones entering into the com- 

 position of the arch. 



The Elephant might have been expected to have had a single superior cava, 

 as have some of the largest existing Rodents, the South American Subungulata, 

 and all other existing large-sized mammals. But it has, like all the Old World 

 and all Nearctic Rodents, two. And it appears that there is some reason for 

 holding that the Proboscidea, in contradistinction to the living Perissodactyla, 

 and to the Artiodactylous Camel, Pig, and Deer, are an Old World type, and 

 to be expected therefore to follow that type in such particulars as the one specified. 



The Elephant however has the symphysis of the lower jaw perfectly anchy- 

 losed ; it is more entirely testicondous ; its brain is richly convoluted, as indeed 

 are the brains of most existing mammals of large size except the Manatee, and its 

 placenta is zonary. 



The zonary form of the placenta similarly distinguishes the Hyracoidea from 

 the Rodentia whilst uniting them more or less with the Proboscidea. In the 

 structural composition of the malar arch Hyrax agrees with the two orders just 

 mentioned, and differs from the Ungulata, but on an estimate such as is given by 

 Brandt (Mem. Acad. Sci. St. Pe"tersbourg, 1869, Tom. xiv) of the sum total of the 

 affinities of this animal, it should be ranked as an Ungulate with Rodent ward 

 affinities rather than as a Rodent. Brandt's own words run thus, p. 119 : * Es 

 werden daher die Hyracen im Allgemeinen wohl am passendsten als Ungulata 

 gliriformia oder glirioidea bezeichnet und als eine, jedoch weit mehr den Huft- 

 thieren ahnliche, Mittelform zwischen den genannten Thieren und den Glires 

 angesehen werden konnen.' On another page, p. 116, Brandt suggests that Hyrax 

 may connect the ' Pachyderms,' by which he in this connection means the Perisso- 

 dactyla, with the Sciuromorphous Rodents specially, and also with the Lagomor- 

 phous, whilst the Mesotherium would stand similarly in relation to the Lagomorphi 

 and the larger animals in question. Andreas Wagner indeed had expressed himself 

 in 1844 in opposition to Cuvier, and to the same effect as Brandt, by saying that 

 a separate family should be created for Hyrax amongst the Pachyderms, and that 

 it should be considered as forming a transition towards the Rodents. 



Cuvier, as is well known, in opposition to the view which trivial names, 

 such as that of l Marmotte bdtardj given to Hyrax, embodied, went so far as to 

 speak of it as being a dwarf Rhinoceros, and in his Ossemens Fossiles, ii. p. 127 

 seqq. 1822, he enumerates certain points of resemblance between the two animals. 

 These points are such as the number, 20-21, of the ribs, as the transverse direction 

 of the condyle of the lower jaw, as the absence of canines, as the shape of the 

 nails, and as the presence of but three toes on the hind feet, and are inadequate 

 to the support of such a view as the epigrammatically stated one just quoted. His 



