BRADTPID^E. MAMMALIA. BRADYPID.E. 



153 



very nearly twice as long as the hinder extremities, 

 and in this feature we are inevitably reminded of a 

 similar arrangement in the limbs of certain quadru- 

 mana whose habits are in some respects analogous to 

 those of the family under consideration. On closer 

 inspection of the hands, it will be noticed that the 

 bones of the carpus and metacarpus are short and 

 ankylosed together, whilst the terminal digits are 

 long, and furnished with immense hooked claws. 

 These prehensile talons are closely curved towards the 

 palm while not in use, or in a state of rest ; but when 

 the animal requires to grasp a fresh branch, they are 

 forcibly extended by muscular contraction, assuming 

 a position like that given hi the raised arm of the 

 accompanying representation, above referred to. The 

 hind feet are similarly constructed, and a glance at 

 their position, with the soles directed obliquely inwards, 

 is sufficient to show how unnatural it is to represent a 

 Sloth walking all-fours on a plain level surface. In the 

 older natural history collections of the United Kingdom, 

 nothing is more common than to observe the errors 

 into which taxidermists have fallen in mounting and 

 displaying the stuffed skins of Sloths; and we could 

 still point to fine collections where the tardigrade 

 edentates may be seen sprawling on the floor in the 

 most approved style, with their backs toward the sky ! 

 Having personally inspected, with care, the principal 

 museums of natural history in London, Edinburgh, 

 Glasgow, and Dublin, we have no hesitation in saying 

 that, if any one wished to see the way in which Sloths 

 ought to be stuffed, they would do well to take a 

 glance at the specimens preserved hi the museum of 

 Trinity College, Dublin and they are not the only 

 evidences of taxidermal skill to be seen hi the Irish 

 capital. But, to return to our skeleton, and the 

 figure reduced from that given in Cuvier's celebrated 

 " Ossemens Fossiles " let us next examine the head 

 (fig. 52). Here we have a striking contrast when 

 compared with the attenuated crania of the ant-eaters. 



Fig. 52. 



Skull of the Sloth. 



The Sloth's head is short, rounded, flat, and truncated 

 at the muzzle ; the jaws are generally furnished with 

 eighteen molar teeth the anterior pair, above and 

 below, having been regarded by Cuvier as incisors; 

 the .young individual carries twenty molars. In the 

 construction of the bones of the trunk, and especially of 

 the pelvis, we notice other interesting adaptations to the 

 peculiar habits of these creatures ; but among these we 

 have only space to mention the remarkable elongation 

 VOL. I. 



of the neck. This cervical extension was at one time 

 supposed to be due to the presence of nine true neck- 

 vertebrae; but some years since, Professor Bell satis- 

 factorily demonstrated, from prepared skeletons in his 

 own collection, that the so-called eighth and ninth 

 cervical veretebrse were, in reality, true dorsal segments, 

 seeing that he had discovered a pair of little rudi- 

 mentary ribs attached to each of the osseous elements 

 in question. " The object," says Mr. Bell, " of the 

 increased number of vertebrae in the neck, is evidently 

 to allow of a more extensive rotation of the head ; for, 

 as each of the bones turns to a small extent upon the 

 succeeding one, it is clear that the degree of rotation of 

 the extreme point will be in proportion to the number 

 of movable pieces in the whole series. When the 

 habits of this extraordinary animal are considered, 

 hanging as it does from the surface of boughs with the 

 back downwards, it is obvious that the only means by 

 which it could look towards the ground must be by 

 rotation of the neck ; and as it was necessary, in order 

 to effect this without diminishing the firmness of the 

 cervical portion of the vertebral column, to add certain 

 movable points to the number possessed by the rest 01 

 the class, the additional motion was acquired by modi- 

 fying the two superior dorsal vertebrae, and giving 

 them the office of cervical, rather than infringing on a 

 rule which is thus preserved entire without a single 

 known exception." As we shall immediately have 

 occasion to return to the consideration of the habits of 

 these animals, we have here only further to observe 

 that the Sloths are all natives of the forests of South 

 America, where they feed upon vegetable matters, 

 chiefly leaves. The extinct genera, Megatherium, 

 Megalonyx, Scelidotkerium, Erinathopsis, and Erep- 

 todon, are also referable to this family, forming the 

 subdivision of gravigrade edentates. 



THE AI (Bradypus tridactylus) or THREE-TOED 

 SLOTH Plate 17, fig. 55 is the best known of all the 

 species. The specific term applied to it rests upon the 

 arbitrarily assumed grounds that it is the only species 

 which is furnished with the three toes; but there is 

 every reason to believe that at least two other Sloths 

 the B. gularis of Pvuppell, B. torquatus of Illiger, and 

 B. infuscatus of Wagler being regarded as so many 

 distinct species have tridactylous feet. Be this as it 

 may, the generality of naturalists appear content to retain 

 the old Linnaean appellation, and we shall not deviate 

 in the present instance from their combined authority. 

 The Ai inhabits the most secret recesses of the South 

 American forests. The body is enveloped by a coarse 

 shaggy fur, and so disposed about the short round 

 head, as to impart to the physiognomy a human look. 

 The fur has a greyish colour generally, young indi- 

 viduals being frequently spotted with brown and white; 

 the under parts have usually a light fulvous tint. 

 When describing the skeleton, we took occasion to 

 remark somewhat on the habits of this animal, and 

 especially referred to its awkward behaviour when placed 

 on a level surface. One of the most singular errors 

 into which the great French anatomist fell, was that 

 of ascribing to the Ais deficiencies and imperfections 

 of organization, as if they were not well adapted to the 

 mode of existence which the Creator had been pleased 



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