SLOTHS. 
97 
Order X. EDENTATA. 
The Edentata as a whole are characterized by the incomplete [Case 23.] 
state of their dentition. In many forms teeth are entirely absent, 
while when present they are always composed of dentine and 
cement only (without enamel), and never form roots. In only one 
genus {Tatusia) is there a functional milk -dentition, one only 
(Dasypus) possesses premaxillary teeth, and in none is there any 
definite division of those in the maxilla into canines, premolars, and 
molars. 
The first family, the Bradypodidoi, or Sloths, have short round 
heads, five teeth above and four below. The vertebrae, owing to 
the inactive habits of Sloths, are almost entirely devoid of neural 
spines, and the whole vertebral column, especially in the neck 
region, is remarkably flexible and loosely united. The cervical 
vertebrae, which in all other Mammals, except the Manatee, are 7 
in number, amount to no less than 9 in the Three-toed Sloths 
[Bradypus) , while in certain of the Two-toed Sloths [Choloepus) 
there are only 6. In Cholcepus the clavicle is attached to the cora- 
coid, a peculiarity not occurring in any other Mammal. The pelvis 
is remarkable for being united to an unusually long portion of the 
spinal column, both the ilium and ischium being attached by bone 
to the latter. In old animals most of the carpal and tarsal bones 
ankylose together. In addition to the difference in the number 
of their claws, the two genera Bradypus and Cholcepus are also 
readily distinguished by the different shape and proportions of their 
teeth, — those of the former being small, of equal size, and the upper 
ones placed opposite the lower, so that they wear down nearly flat ; 
while in Cholcepus the first tooth in each jaw forms a sort of canine, 
twice as long as any of the others, and as the teeth are placed 
alternately in the two jaws, they are worn down into wedge-shaped 
crowns. 
Skeletons and skulls of both Bradypus and Cholcepus are placed 
in Case 23, Div. E. 
Intermediate to a certain extent between the Sloths and Ant- 
eaters are certain huge fossil animals, found in the post-Tertiary 
deposits of South America, of which the best known is the Great 
Ground-Sloth [Megatherium americanum), of the complete skeleton 
of which a cast is exhibited in the Geological Gallery. 
H 
