The chevron-bones in the tail surround a well-developed rete mirabile, a rete being found in precisely the same position in the Eastern _Manis_. _Tamandua_ has also retia, which are also found in the Spider-monkeys. _Cycloturus_ is by far the smallest of the Anteaters. It has {170} only two toes on the fore-feet. It is to be distinguished, anatomically, from its larger relatives by the complete clavicle, and by the fact that the pterygoids do not meet in the middle line of the skull. The ribs, too, are unusually wide, as in the Whale _Neobalaena_, and form a bony encasement for the body. It has two small caeca. Of fossil Anteaters but little is known. The most interesting form is _Scotaeops_, interesting because it has two small back teeth, which are totally lost in its living allies. The huge Patagonian extinct bird _Phororhacos_, first known by a lower jaw, was at one time regarded as a member of this group on account of the form and edentulous character of the jaw. [Illustration] FIG. 96.--Unau, or Two-toed Sloth. _Choloepus didactylus._ x 1/5. (After Vogt and Specht.) {171} [Illustration] FIG. 97.--Skull of Three-toed Sloth. _Bradypus tridactylus._ Lateral view. _fr_, Frontal; _ju_, jugal; _lcr_, lachrymal; _max_, maxilla; _nas_, nasal; _par_, parietal; _s.oc_, supra-occipital; _ty_, tympanic. (From Parker and Haswell's _Zoology_.) FAM. 2. BRADYPODIDAE.--The Sloths, genera _Bradypus_ and _Choloepus_, come, as already stated, very near to the Anteaters, in spite of their striking difference in appearance. The Sloths are purely arboreal creatures, with strong recurved claws, which serve as hooks to keep them suspended from the lower side of a branch. The three-toed sloth, _Bradypus_ (or "Ai"), has the exceptional number of nine cervical vertebrae; the two-toed sloth, _Choloepus hoffmanni_ (or "Unau"), has the equally exceptional number of six. The hair is long and shaggy, and gets an adventitious green colour from the presence of minute algae.[107] This gives to the animal the appearance of a lichen-covered bough, a resemblance which is increased in one species by an oval mark upon the back, which suggests forcibly a broken end of such a branch. The likeness of a Sloth to its surroundings is pointed out by Dr. Siemann,[108] who observed that a species occurring in Nicaragua "has almost exactly the same greyish-green colour as _Tillandsia usneoides_, the so-called 'Vegetable Horsehair' common in the district.... If it could be shown that it frequented trees covered with that plant ... there would be a curious case of mimicry between the sloth's hair and the _Tillandsia_, and a good reason why so few of these Sloths are seen." The stomach in the Sloths is complicated in structure, with several chambers; one of these gives off a long crescent-shaped caecum. The skull of the Sloths agrees in a number of particulars with that of the Anteaters. {172} [Illustration]