1 82 MAMMALIA ORDER IX. EDENTATA* 



to the absence of front teeth common to all members of the order, but fir may 

 be stated that the cheek-teeth grow throughout life and thus never develop 

 roots; while it is but very rarely that milk-teeth are present, and in only a 

 single instance do these cut the gum. With the exception of the sloths, in 

 which they have probably been lost, the hinder vertebra) of the trunk have 

 additional articular surfaces. In their whole organisation the edentates 

 display a low type, as is exemplified by the generally small size of their 

 brains, in which there are usually but few convolutions on the surface. 



The sloths, or Bradypodidce, form a small family of edentates specially 

 characterised by their adaptation to an arboreal life, and differing from nearly 



all other mammals by their habit of hanging back-downwards 

 Sloths. from the branches of the trees on which they dwell. They 



are comparatively small, slenderly-built animals, with a 

 peculiarly rough, shaggy coat, a short, rounded, and almost sperical head, 

 and inordinately long and slender limbs especially the fronfc pair 

 terminating in huge, hook-like claws. The small ears are completely buried 

 among the long fur covering the head ; and the tail is rudimental. The 

 cheek-teeth, which comprise five pairs in the upper and four in the lower 

 jaw, form short cylinders, of which the external layer is harder than the 

 central core, so that by use their grinding surfaces become slightly cupped. 

 \Vhereas, however, in the three-toed sloths the whole of the teeth are of 

 this simple type, in the two-toed species the first pair in each jaw are taller 

 than the rest and assume a somewhat tusk-like form, with their summits 

 obliquely bevelled by mutual wear. In the limbs the narrow and curved 

 feet are reduced to the condition of little more than hooks ; the three-toed 

 forms having three claws on each foot, whereas in the other group 

 the number of claws in the fore feet is reduced to two. Although 

 admirably adapted for suspending the animal back downwards from a 

 branch, the feet of the sloth are but poor instruments for progression on the 

 ground, and when walking, a sloth advances awkwardly and slowly, with the 

 soles turned inwards. Externally the fur of the sloth is of a dull brownish 

 or ashy colour, the individual hairs having a fluted outer surface. The most 

 extraordinary feature about the fur is, however, the growth of a vegetable 

 substance on the surface of the hairs, thus increasing the resemblance of the 

 animal, when hanging at rest from a bough, to a rough lichen-clad knot. 

 Beneath the outer coat of long grey hairs is a finer under-fur marked by 

 longitudinal stripes of chocolate-brown and orange ; a patch of this under-fur 

 being frequently exposed in the middle of the back by the habit these 

 creatures have of rubbing or resting this part of their bodies against the 

 trees. In conformity with the shape of the skull, the soft tongue is very 

 short. The female has the single pair of teats situated on the breast. 

 Internally sloths are specially characterised by the complexity of their 

 stomachs, and a peculiar folding of the windpipe. Sloths are divided into 

 two distinct generic groups. Of these, the three-toed sloths (Bradypus) are 

 characterised by having three toes to each foot, and all the teeth short and 

 cupped, whereas in the two-toed sloths (Cholcepus), there are only two toes on 

 the fore feet, and the front pair of teeth in each jaw are taller than the 

 others and obliquely bevelled at the summits. Very exceptional among 

 mammals are the sloths in regard to the number of vertebrte in the neck. 

 Thus, whereas in one of the two-toed kinds there are the normal seven, in a 

 second the number is reduced to six ; while in the three-toed group there are 

 invariably nine of these segments. 



