Sloths.J 



MUSEUM OF ANIMATED NATURE. 



175 



ORDER EDENTATA. 



Cuv. (Bruta, Linn.) This order, which contains 

 the Sloths, the extinct Megatherium and Mylodon, 

 the Armadillo, the Pangolin, and the Ant-eater, 

 appeals at a first glance to be less natural than upon 

 careful analysis it is proved to be. Several import- 

 ant links indeed, the absence of which left voids in 

 the chain, have fortunately been recovered, their 

 fossil relics restored, and the species assigned to 

 their true place. In this philosophic labour Pro- 

 fessor Owen has rendered to science the most import- 

 ant service, and his work, entitled a ' Description of 

 the Skeleton of an extinct gigantic Sloth, but which 

 is in fact an elaborate analysis of the structure and 

 affinities of the megatheroid quadrupeds in general, 

 is a monument of research and acumen. 



With respect to the term Edentata (toothless ani- 

 mals) it must be taken in a qualified sense. The 

 a.nt-eaters and pangolins are indeed destitute of teeth, 

 but. the other genera possess these organs with cer- 

 tain limitations as to number, and of peculiar struc- 

 ture, wanting both the neck part and enamel. 

 Without further preface we may observe that the 

 Edentata resolve themselves into two great sections, 

 namely, Leaf-eaters and Insect or Flesh-eaters. 

 These sections, from their respective habits, have 

 been termed by Desmarest, Tardigrada, or slow- 

 paced, and Effodimtia, or diggers: but to these 

 terms, as they are not universally applicable to the 

 .species they include, there are some objections. 



I. LEAF-EATERS. 



Family Sloths (Tardigrada, Owen ; Bradypolidse 

 Auct.). 



Genus Bradypus, Linn. (Adieus, F. Cuv.)— Claws 

 •on the fore-feet, three. 



768, 769, 770.— The Common Sloth, or Ai. 

 (Bradypus tridaetylus, Linn.). The Sloths are crea- 

 tures as extraordinary in their habits as in their 

 organization, the one having a mutual relationship 

 to the other. They are exclusively arboreal ; the 

 trees afford them at once their needful food and 

 their permanent abiding-place : and for the trees 

 alone are they structurally adapted. It is not long 

 since that the sloth was condemned as a degraded 

 miserable being ; slow and embarrassed in all its 

 movements, and wretchedly framed, as if Nature 

 had bungled in its creation. Inconsistent with phi- 

 losophy, and presumptuous in the extreme, is such 

 a,n opinion. The tall giraffe and the sinewy-limbed 

 antelope are not more directly organized for their 

 respective requirements, than is the sloth for its 

 appointed place in the scale of creation. Were it a 

 terrestrial animal, then indeed might we call its 

 structure defective ; but, its mode of life taken into 

 consideration, we view it in another light, and per- 

 ceive that it affords a marked example of design 

 and purpose. 



Button's eloquent misrepresentation of the sloth 

 need not detain us, but we cannot avoid expressing 

 our surprise that the great Cuvier not only quotes 

 the words of that naturalist, but even follows up his 

 ideas. The only excuse is, that the habits of the 

 animals till recently were very imperfectly under- 

 stood ; yet might we not expect that a philo- 

 sopher would pause before concluding that in 

 the works of nature there occurred exceptions 

 to the Jaws of harmony by which the whole is 

 governed ? 



A few observations on the organization of the 

 sloth may not be unacceptable. 



Fig. 771 represents the skeleton of the common 

 three-toed sloth ; Fig. 772 the pelvis of the same ; 

 Fig. 773 the skeleton of the Unau, or two-toed 

 sloth. 



In the skeleton of the sloth we are struck at once 

 with the great length of the fore-limbs, which are 

 twice as long as the hinder pair, and with the huge 

 hook-like claws by which all four are terminated : 

 we perceive, too, that the pelvis is bird-like in its 

 conformation and of great breadth, separating the 

 thigh bones to an unusual distance from each other ; 

 added to this, the thigh bones are directed obliquely 

 outwards, while the limb from the knee downwards 

 has an inward inclination ; and the structure of the 

 wrist and ankle is such, that the palm or sole, in- 

 stead of being directed to the surface of the ground, 

 as in other animals, is turned inwards towards the 

 body in such a manner as to render it impossible 

 for the sloth to place the sole of its foot straight 

 down on a level surface, but to compel it under 

 such circumstances to rest upon the external edge 

 of the foot (see skeleton, Fig. 771). The hip-joint, 

 as in the orang-outan, is destitute of the ligamen- 

 tum teres, whence the head of the thigh bone is 

 endowed with greater freedom of motion. In the 

 Ai (three-toed slotft) the neck consists of nine 

 vertebrae, instead of seven, the. ordinary number in 

 mammalia, and the two tables of the skull in all 

 the species are separated by large air-cells, so that 

 the small bird-like brain is defended by a double 



case, a provision against accidental falls, should 

 the branch to which the animal is clinging give 

 way. 



Professor Owen observes, respecting the sloths, 

 that " they illustrate the affinity or tendency to the 

 oviparous type, by the supernumerary cervical ver- 

 tebrae, supporting false ribs, and by the convolu- 

 tion of the windpipe in the thorax, in the three- 

 toed species ; by the lacertine (lizard-like) character 

 of three and twenty pairs of ribs in the unau ; and 

 by the low cerebral development, by the great 

 tenacity of life, and long-enduring irritability of 

 muscular fibre in both species." The muscles of 

 the sloth are endowed with the most aston- 

 ishing energy ; their force is, indeed, almost in- 

 credible, and harmonizes with the arboreal design 

 of the skeleton, of which the limbs alone sufficiently 

 indicate the creature's habits. Who can mistake 

 the meaning of the solid hook-like structure of the 

 paws, or the design of the long arms, or of the 

 security of the union of the clavicle to the large 

 scapula ? We might here enter into minute de- 

 tails, but we refrain, only observing that Nature in 

 these points aimed at rigid unyielding strength, and 

 has obtained the result she wished ; the long arms 

 of the sloth being thus furnished with strong hooks, 

 which are drawn to the palm (and the same obser- 

 vation applies to the claws of the hind-feet) by 

 means of elastic ligaments it can reach to a distant 

 branch, and there fix itself with facility, or, while 

 clinging to one branch, can draw towards itself 

 another loaded with buds, fruits, or leaves, which 

 offer a grateful repast. Rigid as its paw is, it can 

 use it as a hand, and with great address convey 

 food to its mouth. 



Unfitted then for the ground, on which he 

 can only drag himself along by applying the claws 

 of the fore-feet to any rough projection within reach, 

 the sloth is eminently qualified for the branches of 

 the forest, and that rather for their upper than 

 their under surface ; clinging to them, he rests 

 and travels suspended, yet in perfect security ; here 

 his awkwardness disappears, and he traverses the 

 branches or passes from tree to tree in the dense 

 forest with considerable celerity, either in quest of 

 food, or in order to escape his enemies. Stedman, 

 in his ' History of Surinam,' has an engraving of a 

 sloth in this position, which we have copied as 

 illustrating its singular mode of progression (Fig. 

 770). But the arms of the sloth are also his wea- 

 pons of defence, and weapons of no little force : 

 when attacked on the ground, he throws himself on 

 his back, fixes his claws on his adversary, and 

 grasps him with enormous power ; in this manner 

 lie has been known to strangle a dog, holding him 

 all the while at arm's length, and in this manner he 

 grapples with snakes of large size, to the attacks of 

 which he is said to be subject. 



Mr. Burchell (says Professor Buckland, in an 

 interesting paper on these animals in the ' Linn. 

 Trans.' 1835) observed, that " his captive sloths 

 assumed during sleep a position of perfect ease 

 and safety on the fork of a tree, their arms em- 

 bracing the trunk, their backs resting on the angle 

 of a branch, and their head reclining on their 

 own bosom. The animal is thus rolled up nearly 

 in the form of a ball; the entire vertebral co- 

 lumn, including the neck, assumes a nearly cir- 

 cular curve, and not only is the weight of the 

 whole body maintained in an attitude of ease and 

 safety, but the head is supported between the 

 arms and chest, and the face hes buried in the long 

 wool which covers those parts, and is thus pro- 

 tected during sleep from the myriads of insects 

 which would otherwise attack it." According to 

 Mr. Burchell, the buds and young shoots of a spe- 

 cies of Cecropia form the principal food of the 

 sloth. These trees grow only in damp places, and 

 rise with a slender stem to the height of thirty or 

 forty feet, giving off horizontal branches, hollow 

 internally, except at the extremities. Along these 

 branches" it travels, and the young cling round the 

 body of the mother. It would appear that the 

 moisture of leaves or buds suffices the sloth for 

 drink, as none kept by Mr. Burchell took liquid in 

 any other way. In the aspect of the sloth there is 

 an expression of profound melancholy ; it seldom 

 utters any cry ; it notices nothing with any positive 

 mark of attention except perhaps the trees to which 

 unerring instinct draws it, nor by any action evinces 

 much intelligence. 



The dental system of the sloth is the most simple 

 that can well be conceived. They have no incisor 

 teeth, but canines and molars only ; and in the Ai 

 the canines are diminutive, and in all respects very 

 similar to the other teeth. The molar teeth are 

 universally eight in the upper jaw and six in the 

 lower, four and three on either side respectively. 

 Their construction is most simple ; they are cylin- 

 drical, unrooted, consisting, as Professor Owen has 

 demonstrated, of a centre of vascular dentine sur- 

 rounded by unvascular dentine or ivory, the whole 

 enveloped by a layer of caementum, characterised 



by numerous minute calciferous cells. Ill fitted for 

 grinding the food, the teeth merely bruise it or break 

 down the tender structure of the buds or leaves, 

 their deficiency in this point being most probably 

 compensated by the singular complication of the 

 stomach, which is sacculated. 



The sloths bring forth and suckle their young 

 like ordinary quadrupeds. They have two mammas, 

 which are situated on the breast ; and the young- 

 sloth, from the moment of its birth, adheres to the 

 body of its parent till it acquires sufficient size and 

 strength to shift for itself. The head of the Ai is 

 short, the face small and round like that of the Ame- 

 rican monkeys, the ears concealed in the long hair 

 which surrounds them, the eyes small and deeply 

 sunk in the head, and the tail a mere rudiment. 

 The Indians like its flesh, and are in continual 

 pursuit of it. 



Naturalists reckon two distinct species of the Ai, 

 and three or four varieties, some of which may pro- 

 bably be found to be specifically different, when 

 they come to be dissected and carefully compared 

 with one another. 1. The common Ai (Bradypus 

 tridaetylus, Linn.) has a short round head, furnished 

 with coarse shaggy hair, disposed on the crown in 

 verging rays, like that of the human species ; the 

 face is of a yellowish colour covered with very 

 short hair, whilst that of the body and extremities 

 is universally long and shaggy ; the eyes are en- 

 circled by a brown ring ; the hair of the body varied 

 with irregular patches of dark and light brown, or 

 silvery white : between the shoulders there is an 

 oval patch of short orange-coloured hair, of a finer 

 quality than that found on other parts of the body, 

 and divided in the centre by a longitudinal black 

 stripe ; the throat and breast are frequently of a 

 light straw-colour. The texture of the hair is 

 altogether peculiar, and more nearly resembles dry 

 hay, or grass shrivelled and withered by the sun, 

 than the hair of ordinary quadrupeds. It is coarse 

 and flattened at the extremity, but as small at the 

 root as the finest spider's web ; and its dry and 

 withered appearance forms the Ai's principal se- 

 curity against its pursuers, as it renders it extremely 

 difficult to detect it, whilst at rest among the 

 branches covered with bark and moss of the same 

 colour ; it is only when in motion that it can be 

 readily distinguished from the trunk beneath which 

 it hangs suspended. In other respects, different 

 individuals of this species differ considerably from 

 one another, in the shade and disposition of their 

 colours, and in the intensity of the mark between 

 the shoulders; some even want this latter mark 

 altogether, others are of a uniform ash-colour over 

 the whole body, and there are others still, which 

 have the hair of the head parted in the centre, and 

 hanging down upon each side. 



Length of the adult about seventeen or eighteen 

 inches. 



The Collared Ai, (Bradypus collaris,) is a very 

 distinct species, even in the bony structure of its 

 cranium. Its face is naked and of a black colour; 

 the hair of its body less flattened and withered-look- 

 ing than in the common species; the forehead, 

 temples, chin, throat, and breast covered with red- 

 dish or rust-coloured hair, slightly frizzled ; on the 

 crown of the head it is long and yellow, and on the 

 rest of the body pale orange : but the most dis- 

 tinguishing mark of the species is a large black 

 collar which completely surrounds the neck, and 

 from which its specific name of collaris is derived. 

 Beneath this outer coat there is an inner one of 

 very fine fur, which is of a dark brown colour on the 

 collar, but gradually diminishes in intensity towards 

 the croup, where it is 'entirely white. 



Both these species feed upon the leaves of trees, 

 and bring forth but a single young one at a birth. 

 When in motion in the forests they emit a feeble 

 plaintive cry, resembling the word Ai, and which is 

 the origin of the name they bear among the Eu- 

 ropeans settled in America. They are extremely 

 retentive of life, and have been seen to move their 

 legs, and exhibit other symptons of vivacity, a full 

 half- hour after being deprived of the heart and other 

 viscera. 



The Unau, or two-toed sloth, of which we figure 

 the skeleton (Fig. 773), is placed by Illiger in a dis- 

 tinct genus, under the title of Choloepus. It is the 

 Bradypus didactylus of Linnaeus. In its manners it 

 closely resembles the Ai, which it exceeds in size. 



In both genera the skull is rounded, and the 

 muzzle short, but more especially in the Ais. The 

 zygomatic arch is very bold and stout, but is incom- 

 plete in the centre. The malar bone is very deve- 

 loped, and gives off a descending branch reaching 

 over the lower jaw, but its zygomatic process does 

 not reach the corresponding process of the temporal 

 bone ; hence the arch, as we have said, is imperfect. 

 The orbits are nearly circular, but incomplete be- 

 hind. The lower jaw is large and strong. 



In the two-toed sloth there are no pro-dorsal or 

 supernumerary vertebrae in the neck ; the feet are 

 far less universally consolidated together. 



