74 



KNOWLEDGE. 



[April 2, 1894. 



and, indeed, were it not for the extinct creatures forming 

 the subject of the present article, it would have been very 

 difficult to discover how close the connection between these 

 two groups really is. In place of the short and rounded 

 heads of the sloths, the anteaters have the head greatly 

 elongated and very slender, while the thin jaws are totally 

 devoid of teeth, and the tongue is long, cyhndrieal, and 

 highly extensile. There is, however, some degree of 

 variation in regard to the degree of elongation of the 

 skull, the maximum development occurring in that of the 

 great anteater. If possible, a still greater difference 

 obtains in the structure of the feet, the fore foot of the 

 great anteater having five toes, of which the middle one 

 is vastly more powerful than either of the others ; while 

 all but the fifth have strong claws. In walking, the 

 extreme outer side and part of the upper surface of the 

 fore foot are applied to the ground ; but in the hind foot, 

 which has the fourth toe the largest, and all the five digits 

 furnished with claws, 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 circum- 

 stance that the bones of the terminal joints of the feet 

 have a longitudinal median groove on the upper surface 

 at their tips. 



With these preliminary remarks on some of the leading 

 featin-es of the sloths and anteaters, 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 Mefiatherium, of 

 which a nearly complete skeleton was discovered in the 

 year 1789 near Lujan, in the province of Buenos Ayres. 

 This skeleton was soon after sent to Madrid, and described 

 by Cuvier in 1798, who gave to the animal to which it 

 belonged the name by which it has ever since been known. 

 If we desired to be hypercritical, we might convict the 

 great anatomist of not having formed this name accordmg 

 to strict rule, for it ought clearly, as in the analogous 

 instance of Mei/alosauriis, to have been Me(jalotherium, 

 instead of Meiiatherium ; but let this pass. Cuvier recog- 

 nized the aftinities of the megathere to the sloths ; and 

 other skeletons subsequently obtained fi-om the Pleistocene 

 deposits of Buenos Ayres, and which are now in the 

 museum of the Eoyal 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 

 somewhere about eighteen feet in total length, the 

 megathere, although having a rather more elongated 

 skull, agrees with the sloths in the number of its 

 teeth. In structure, however, these teeth, of which 

 the four lower ones are represented in the accompanying 



a length of over ten inches, and a diameter of fully 

 an inch and a half. The summit of each individual 

 tooth carries a pair of transverse ridges, produced by 

 the alternation of vertical plates of diii'erent hardness m 

 the tooth itself ; and since the teeth are rootless and 

 grow continuously throughout the life of their owner, 

 this transversely-ridged structure is likewise permanent. 

 To contain such enormous teeth, the lower jaw is remark- 

 ably deepened in the middle of its length, where it 

 descends suddenly. The long median channel shown in 

 our figure extending between and in front of the anterior 

 teeth, is e\-idently for the reception of a large and fleshy 

 tongue, which from its size was probably extensile like 

 that of the giraffe. 



If we had only the megathere to deal with, we might 

 have some hesitation, judging from the skull and teeth 

 (which in the group are the only portions of the skeleton 

 showing sloth-like affinities), in regarding the group of 

 animals to which it belongs as closely allied to the sloths. 

 Fortimately, however, the same Pleistocene deposits of 

 Buenos Ayres (to say nothing of the caverns of Minas 

 Geraes, in Brazil) have yielded us remains of other and 

 somewhat smaller ground- sloths, known as mylodonts, 



Fio. 1.— Upper surface of the Lower Jaw of the Megathere. 

 One-eighth natural size. (After Owen.) 



figure of the lower jaw, are decidedly different to those 

 of the sloth. In form they are square prisms, with 



Pig. 2.— Under view of the Skull of a Mvlodont. 

 One-sixth natural size. (After Owen.) 



which effectually bridge, in these respects, the gap 

 between the megathere and the sloths. In these animals, 

 as shown in our second illustration, the teeth are either 

 cylindical or triangular in section ; and from having a 

 harder external coat, wear in the same cup-shaped manner 

 as those of the latter. Moreover, in some mylodonts 

 the front pair of teeth in each jaw have the elongated 

 tusk-like form and oblique wear characterizing those of 

 the two-toed sloth, while in others they resemble the 

 hinder teeth, as in the three-toed sloth. We thus have 

 an exact parallelism in this respect among the mylodonts 

 to the two genera of sloths ; and as their skulls in 

 their more rounded and shorter form, and the absence 

 of a descending expansion in the middle of the lower 

 jaw, are likewise more sloth-like than is the skull of 

 the megathere, we can have no hesitation m regarding the 

 ground-sloths, so far as cranial characters are concerned, 

 as closely allied to the sloths. It may be added that the 

 great divergence of the two series of teeth in our figured 

 mylodont skull indicates the presence during life of a 

 tongue of great width and size. 



Thus far we have been showing how the ground-sloths are 

 related to the sloths in the characters of their skulls ; but 

 other members of the group, known as the scelidotheres 

 (Scelidotheyiiim), although still retaining the same number 

 of teeth, show a certain approximation in these respects to 

 the anteaters. Thus their skulls, instead of being short 

 and broad like those of the mylodonts, are very long and 

 narrow, and have the muzzle much produced in advance 



