182 EDENTATA 
and sometimes the eighth, bears a pair of short movable ribs. 
The arms or fore limbs are considerably longer than the hind 
legs. The bones of the fore arm are complete, free, and capable of 
pronation and supination. The hand is long, very narrow, habit- 
ually curved, and terminates in three pointed curved claws, in 
close apposition with each other. The claws are, in fact, incapable of 
being divaricated, so that the hand is reduced to the condition of a 
triple hook, fit only for the function of suspension from the boughs 
of trees. The foot closely resembles the hand in its general struc- 
ture and mode of use; the sole being habitually turned inwards, so 
that it cannot be applied to the ground in walking. The tongue is 
short and soft, and the stomach large and complex, bearing some 
resemblance to that of the ruminating Ungulates. The windpipe 
or trachea has the remarkable peculiarity among mammals—not 
unfrequent among birds and reptiles—of being folded on itself 
before it reaches the lungs. The mamme are two, and pectoral in 
position. 
“ Ai” is the common name given in books to the Three-toed 
Sloths. They were all comprised by Linnzus under the species 
Bradypus tridactylus. More recently Dr. Gray described as many 
as eleven species, ranged in two genera, Bradypus and Arctopithecus ; 
but the distinctions which he assigned both to species and genera do 
not bear close examination. Some are covered uniformly with a 
gray or grayish-brown coat; others have a dark collar of elongated 
hairs around the shoulders (B. forquatus); some have the hair of 
the face very much shorter than that of the rest of the head and 
neck ; and others have a remarkable-looking patch of soft short hair 
on the back between the shoulders, consisting, when best marked, 
of a median stripe of glossy black, bordered on each side by bright 
orange, yellow, or white. There are also structural differences in 
the skulls, as in the amount of inflation of the pterygoid bones, 
which indicate real differences of species; but the materials in our 
museums are not yet sufficient to correlate these with external 
characters and geographical distribution. The habits of all are 
apparently alike. They are natives of Guiana, Brazil, and Peru, 
and one if not two species (B. infuscatus and B. castuneiceps) extend 
north of the Isthmus of Panama as far as Nicaragua. Of the 
former of these Dr. Seeman says that, though generally silent, 
a ‘specimen in captivity uttered’ a shrill sound like a monkey 
when forcibly pulled away from the tree to which it was 
holding. 
Choleyus..—Teeth $; the most anterior in both jaws separated 
by an interval from the others, very large, caniniform, wearing 
to a sharp, bevelled edge against the opposing tooth, the upper 
shutting in front of the lower when the mouth is closed (Fig. 59), 
' Wliger, Prodromus Syst. Mumm. ct Avium, p. 108 (1811). 
