122 MAMMALIA. 



of the first grand division are distinguished by having the inferior projecting angle of the 

 lower jaw subquadrate, 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 Scmridm, and the Muridce or 

 Rats ; the Jerboas evincing several peculiar points of relationship with the Dormice : the 

 ArvicolidcB, or Muskquash, Voles, and Lemmings, together with the Guaffres {Geomys), 

 follow the Muridcs, 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 Cavidcp, 

 or Ca[>ybara, Moco, and Cavies, succeeded by the Chincfiillidep, and lastly by the Hares and 

 Pikas, near which it may be that the Ctenodactyle holds its station. In the terminal genera, 

 or the Lcporida, 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 iu 

 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,— 



EDENTATA,— 



Or quadrupeds without teeth in the fore-part of their jaws, constitute our last princijial 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 a])proximate to the nature of hoofs; 

 also bv 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 [.is 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 



