60 



vertically elongated slightly concave surfaces, to which the anchy- 

 losed proximal and middle phalanges of the strong claw-bearing digit 

 articulate. The ungual phalanx is shorter in proportion to its depth, 

 than in the digitus medius of the fore-foot, and differs in the greater 

 breadth of the upper part of the claw-sheath, and in the straighter 

 cone, or bony core, which supported the claw. The metatarsals of 

 the fourth and fifth toes are much larger than that of the third ; but 

 they support mere rudiments of digits reduced in each to two stunted 

 phalanges, which were doubtless buried like those of the outer digit 

 in the fore-foot in a kind of callous hoof. 



Having completed the description of the skeleton, which is illus- 

 trated by an extensive series of accurate and highly finished 

 drawings, the author proceeds to the comparison of the modifica- 

 tions of the osseous structure of the gigantic extinct animal with that 

 in other known existing and extinct species of the class Mammalia. 



The teeth agree in number, kind, mode of implantation and 

 growth, with those of the Sloth, and their structure is a modification 

 of that peculiar to the Sloth-tribe. All the modifications of the 

 skull relating to the act of mastication, especially the large and 

 complex malar bone, repeat the peculiarities presented by the ex- 

 isting Sloths. There are the same hemispheric depressions for the 

 hyoid bone in the Megatherium as in the Sloth. In the number of 

 cervical vertebrae the Megatherium, like the two-toed Sloth, agrees 

 with the Mammalia generally. In the accessory articular surfaces 

 aflPorded by the anapophyses and parapophyses of the hinder dorsal 

 and lumbar vertebrae, the Megatherium resembles the Ant-eaters 

 {Myrmecophagcs)'. but it does not resemble the Armadillos (Z>«5j/jow5) 

 in having long metapophyses, the peculiar development of which in 

 those loricated Bruta has a direct relation to the support of their 

 bony dermal armour. In the mesozygapophyses of the middle 

 dorsal vertebrae the Megatherium is peculiar. In the small extent 

 of the produced and pointed symphysis pubis it resembles the Sloths; 

 and in the junction of both ilium and ischium with the sacrum, it 

 manifests a character common to the Edentate order ; but in the 

 expanse and massiveness of the iliac bones, it can only be compared 

 with other extinct members of its own peculiar family of Phyllo- 

 phagous Edentata. Its habits necessitating a strong and powerful 

 tail, we find this resembling in its bony structure that of other 

 Edentata with a similar appendage, especially in the independency 

 of the two haemapophyses of the first caudal, a character which ob- 

 tains in the Great Ant-eater and in some Armadillos; but this is 

 no evidence of direct affinity to either of these families ; the habits 

 of the small arboreal Sloths render their eminently prehensile limbs 

 sufficient for their required movements, and the tail is wanting. 

 Had that appendage been proportionally as large as in the Mega- 

 therium, we cannot suppose that the caudal vertebrae would have 

 materially differed from those of other Edentata. 



In the" coalescence of the anterior vertebral ribs with the bony 

 sternal ribs, the Megatherium resembles the Sloths. This essential 

 affinity is still more marked in the peculiarities of the scapula and 



