1 82 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 mammse are two, and pectoral in 

 position. 



" Ai " is the common name given in books to the Three-toed 

 Sloths. They were all comprised by Linnaeus under the species 

 Bradypus tndadylus. 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. torquatus) ; 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. infuscalus and B. castaneiceps) 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. 



Cholcepus. 1 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), 



1 Illiger, Prodromus Syst. Mamm. et Avium, p. 108 (1811). 



