174 SKETCH OF THE HISTORY OF MAMMALIA. 



city, a full half-hour after being deprived of the heart 

 and other viscera. 



The Uriau, or two-toed sloth, of which we figure the 

 skeleton (Fig. 103), is placed by Illiger in a distinct 

 genus, under the title of Cholceptis. It is the Bradypus 

 didactylus of Linnaeus. In its manners it closely resem- 

 bles the a"i, 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 incomplete in the 

 centre. The malar bone is much developed, 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 behind. The lower jaw is large and 

 strong. 



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

 numerary vertebrae in the neck 5 the feet are far less 

 universally consolidated together. 



Family— GRAVIGRA DA, Owen. 



Feet short, very strong, equal or subequal ; fore-feet 

 with five or four toes, of which one or two of the outer- 

 most are unarmed, fit for support and progression ; the 

 rest are armed with huge claws. Zygomatic arch com- 

 plete, clavicles perfect; tail moderate or stout, acting as 

 a fulcrum or prop. 



Such are the characters of this family, as laid down 

 by Professor Owen. It contains the following genera: — 

 Megalonyx^ Megatherium^ Mylodon, Scelidotherium^ 

 Coelodon, and Sphenodon ; of these genera all the species 

 are extinct, and only known from their fossil relics. 



Mylodon robustus. 



From the skeleton of this extinct giant, now preserved 

 in the Royal College of Surgeons, we see that, except 

 that it was formed for tearing down the trees of the 

 forest, and not living in their branches, it was closely 



