68 MOSTLY MAMMALS 
the whole of the short sole touches the ground in the 
ordinary manner. An important difference from the sloths 
is to be found in the circumstance that the bones of the 
terminal joints of the feet have a longitudinal median groove 
on the upper surface at their tips. 
With these remarks on some of the leading features of 
the sloths and ant-eaters, the reader will be in a position 
to appreciate the peculiarities in the structure of the ground- 
sloths, and likewise to understand the appropriateness of 
the name by which they are designated. 
Apparently the first of these extinct animals known in 
Europe was the giant ground-sloth, or Megalotherium, of 
which a nearly complete skeleton was discovered in the year 
1789 near Lujan, in the province of Buenos Aires. This 
skeleton was soon after sent to Madrid, and described by 
Cuvier in 1798, who gave it the name by which the animal 
has ever since been known. Cuvier recognised the affinities 
of the megalothere to the sloths; and other skeletons sub- 
sequently obtained from the superficial deposits of Buenos 
Aires, and which are now in the Museum of the Royal 
College of Surgeons, the British Museum, and the museums 
of Milan, Paris, and La Plata, have in their turn served to 
confirm the general truth of the original determination. 
One of the most gigantic of land mammals, measuring some- 
where about eighteen feet in total length, the megalothere, 
although with a more elongated skull, agrees with the sloths 
in the number of its teeth. In structure, however, these 
teeth are decidedly different from those of the sloth. In 
form they are square prisms, with a length of over ten 
inches, and a diameter of fully an inch and a half. The 
summit of each tooth carries a pair of transverse ridges, 
produced by the alternation of vertical plates of different 
hardness in the tooth itself; and since the teeth are rootless 
