FIG. 98.--Skeleton of Three-toed Sloth. _Bradypus tridactylus._ (After de Blainville.) The zygoma is incomplete, though the part connected with the frontal has a strong downward process like that found in _Diprotodon_ and some other mammals. There is, moreover, a process from the squamosal, though it does not reach the anterior part and thus {173} complete the arcade. The premaxillaries are very small, and are usually lost in dried skulls. Coupled with these points of likeness are some differences. The lower jaw, for instance, has a well-marked coronoid process. The pterygoids do not meet in the middle line. The teeth are five or four in each half of each jaw. There is no trace of a second set. A peculiarity of the Sloths is the enormous number of dorsal vertebrae. There are twenty-three of these in _Choloepus hoffmanni_, but only fifteen to seventeen in the Three-toed Sloth, _Bradypus_. As in other American Edentates, the acromion joins the coracoid. This connexion occurs in both the Two-toed and the Three-toed species. The limbs of these creatures are very long, a concomitant of an arboreal life. The femur has no third trochanter. The genus _Bradypus_, which by reason of the fact that it has not lost the third toe on the manus seems to be more primitive than _Choloepus_, shows another structural feature which does not bear out this conclusion. The trapezoid and the os magnum of the carpus are united, while in _Choloepus_ they are perfectly distinct bones. The intestine has no caecum. There are several species of Sloths. Eminently perfect though the organisation of the Sloth in relation to its particular surroundings appears to us, Buffon selected the animal as the very type of imperfection in nature. "One more defect," he wrote, "they could not have existed."