BRADYPODIDE 181 
trees of their native forests abound ; the concealment thus afforded 
being heightened in some species by the peculiar greenish tint 
of the outer covering—very uncommon in mammals. This is not 
due to the colour of the hair itself, but to the presence upon its 
surface of an alga, the lodgment of which is facilitated by the fluted 
or rough surface of the exterior of the hair, and the growth of which 
is promoted by the dampness of the atmosphere in the gloomy 
tropical forests, as it soon disappears from the hair of animals kept 
in captivity in England. Sloths are nocturnal, silent, inoffensive, and 
solitary animals, and usually produce but one young at birth. They 
appear to show an almost reptilian tenacity of life, surviving the 
most severe injuries and large doses of poisons, and exhibiting 
longer persistence of irritability of muscular tissue after death than 
other mammals. 
In the Bradypodide, as well as in the Myrmecophagide, the 
testes are placed close to each other, lying on the rectum between 
it and the bladder; the penis is quite rudimentary, consisting 
of a pair of small corpora cavernosa, not directly attached by their 
crura to the rami of the ischia, and having a glans scarcely larger 
than that of the clitoris of most mammals, and, as in birds and 
reptiles, without any true corpus spongiosum. In the females of 
both families the uterus is simple and globular ; and the vagina, at 
least in the virgin state, is divided into two channels by a strong 
median partition. The deciduate placenta of Cholepus is composed 
of a number of lobes aggregated into a dome-like mass; and it 
does not appear that the placenta of the Anteaters departs in any 
important characters from this type. According to the late Pro- 
fessor W. K. Parker, the embryos of the Sloths, Anteaters, and 
Pangolins have the stapes of the middle ear in the form of a rod, 
thus showing affinities with a very primitive type of mammalian 
organisation. 
The Sloths were all included in the Linnean genus Bradypus, 
but Illiger very properly separated the species with but two claws 
on the fore feet, under the name of Cholepus, leaving Bradypus 
for those with three. 
Bradypus..—Three-toed Sloths. Teeth usually 2 on each side ; 
no tooth projecting greatly beyond the others; the first in the 
upper jaw much smaller than any of the rest; the first in the 
lower jaw broad and compressed ; the grinding surfaces of all much 
cupped. Vertebre: C9, D and L 20 (of which 15 to 17 bear ribs), 
$6, Cll. All the known species present the remarkable pecu- 
liarity of possessing nine cervical vertebra, 7.c. nine vertebrae 
in front of the one which bears the first thoracic rib (or first 
rib connected with the sternum, and corresponding in its general 
relations with the first rib of other mammals); but the ninth. 
1 Linn. Syst. Nat, 12th ed. vol. i. p. 50 (1766), 
