66 



t. 5, and M. De Blainville, Osteograph. Bradypus, t. 1 ; skeleton, t. 3. 

 f. 1, 2, old and young skull. 



I. Cholcepus didactylus. 



Bradypus didactylus, Linn. ; Cuvier, Oss. Foss. v. 73. t. 6 ; t. 7. 

 f . 3, 5 ; skull, cop. Cuvier, Reg. An. Ilhist. t. 70. f. 2 ; BJainv. Ostiog. 

 Bradypus, t. 1. 1. 3. f. 13 ; Guerin, Icon. R. J. t. 33. f. 2-2 a, skull. 



B. Unau and B. Curi, Link. 



We have three more or less perfect skulls from different-aged indi- 

 viduals of this species. 



The projection in the front of the lower jaw in the young specimen 

 is narrow and acute ; it then becomes thin, wider and rounded at the 

 end, and in the adult skull it is thickened, prolonged, and again be- 

 comes rather more acute. 



In the adult skull there are very large air-cavities between the pari- 

 etes of the bones, and a considerable ca\ity in the pterygoid bone. 



In the younger skull the pterygoid bone is small, and appears to be 

 nearly solid, but there is a very large circular perforation which com- 

 municates with a canity imder the pterygoid bones, which is nearly 

 entirely obliterated in the adult skull ; and the intermaxillary bones 

 of the two yomig skulls are much less projecting than those of the 

 adult one. 



The young skull exhibits a small, distinctly tapering, produced, 

 additional central nasal bone, which is not preserved (or not to be 

 fomid) in the adult one, or in any of the other skulls of the family 

 which have come under my observation. 



The hinder angle of the lower jaw of the two skulls, the one of a 

 young and the other of an adult animal, in the Museum collection, is 

 nearly similar in form. The condyloid process of the young is short 

 and truncated behind, that in the older jaw being produced and bent 

 back at the tip. 



In the British Museum collection there are five skins of adults, two 

 very young, one dry, the other in spirits, and three skulls more or 

 less perfect. 



The very young specimen in spirits in the British Museum is figured 

 in Griffith's Animal Kingdom, and Seba figures thtfcetus from spirits. 



II. Bradypus. ? Acheus pars, F. Cuvier, Dent. Mamm. t. 78 ; 

 Chidrin, Bradypus pars, Linn. Bradypus, Illiger. Tardigradus, sp, 

 Brisson. Arctopithecus, Gesner. 



Hands and feet three-clawed. Skull flattened above on the fore- 

 head. Grinders : front upper small, cylindrical ; front lower small, 

 transverse, compressed. Intermaxillary bones none, or very rudi- 

 mentary. The upper process of the zygomatic arch with a broad 

 process in front, forming a back edge to the orbit. Pterygoids sepa- 

 rate, much-swollen and raised, very thin, enclosing a large vesicular 

 cavity. 



Lower jaw produced in front between the teeth, flattened. 



Cuvier, Oss. Foss. v. 88, described the skull of this subgenus. 



Blainville (Osteograph. Bradypus, t. 3) figured an imperfect skull 

 of a young animal under the name of B. torquatus, but it does not 



