MAMMALIA. 
122 
of the first grand division are distinguished by having the inferior projecting angle of the 
longer jaw suhquadrate, and not tapering to an acute point. In this group, or series, range 
first the Sciuridce, or Squirrels and Marmots, followed by the Dormice, and next by the 
Jerboas, which latter require to be interpolated between the Sciuridce, and the Muridce or ' 
Rats ; the Jerboas evincing several peculiar points of relationship with the Dormice ; the 
Arvicolid(B, or Muskquash, Voles, and Lemmings, together with the GuafFres (Geomys), 
follow the MuridcB, and then succeed two isolated genera, — Castor and Helamys, which seem 
to constitute particular families : all these successive groups being readily distinguishable by 
the structure of the cranium and inferior jaw, combined with other characters. The members 
of the next great group have the inferior angle of the lower jaw acute, and usually four equal 
molars on each side above and below, having their folds of enamel gradually more complex. 
Abrocoma, Octodon, Poephagomys, Ctenomys, Capromys, Echymys, Myopotamus, Aulacodon, 
then Hystrix and its allies, and near to the last Ccelogenys and Dasyprocta, form a very intel- 
ligible series, after which the bony palate contracts anteriorly, and we arrive at the Cavidce, 
or Capybara, Moco, and Cavies, succeeded by the ChinchiUidcB, and lastly by the Hares and |M 
Pikas, near which it may be that the Ctenodactyle holds its station. In the terminal genera, ^ -■ 
or the Leporidas, the angle of the jaw suddenly ascends. It is probable that multitudes of | 
existing rodents still remain to be discovered, a knowledge of some of which may assist in |r| 
improving the general arrangement. But few have hitherto been met with in the ancient » ? 
tertiary deposits, and those of genera still extant, as that of the Dormice in particular.] | ■■ 
THE SIXTH ORDER OF MAMMALIANS,— | 
i 
EDENTATA,— | 
Or quadrupeds without teeth in the fore-part of their jaws, constitute our last principal divi- | 
sion of unguiculated animals. Although brought together by a purely negative character, 
they have, nevertheless, some positive mutual relations, particularly in the great claws which ; 
encompass the ends of their toes, and which more or less approximate to the nature of hoofs ; 
also by a certain slowness, or want of agility, obviously arising from the peculiar organization 
of their limbs. There are certain tolerably well-marked intervals, however, in these relations, 
which subdivide the order into three tribes. 
The Tardigrada 
Compose the first of these divisions. They have a short face. The name refers to their 
excessive slowness, consequent upon a construction truly heteroclite, in which nature seems 
to have amused herself by producing something imperfect and grotesque. [A most strange 
assertion on the part of Cuvier, originating from a want of knowledge of the peculiar habits 
of these singular animals.] The only existing genus is that of 
The Sloths [as they are badly named] {Bradypus, Lin.), — 
Which have cylindrical molars, and sharp canines longer than these molars ; two pectoral mammae ; 
and the toes completely joined by the skin, and only marked externally by enormous compressed and 
crooked claws, which, when at rest, are always bent towards the palms, or soles, of the fore and hind 
feet. The latter are obliquely articulated on the leg, and apply only their outer edge ; the phalanges 
of the toes are articulated by serrated ginglymi, and the first, at a certain age, becomes soldered to 
the metacarpal or metatarsal bones, which also, for want of use, become similarly anchylosed. To this 
inconvenience [ ? ] in the organization of the extremities is added another, not less great, in their 
proportions. Their arms and fore-arms are very much longer than their thighs and legs, insomuch 
