47 



that species, viz. the Unau, which we have already seen to have deviated 

 least from the Megatherian type in the form of its skull, and shall sub- 

 sequently find to present a closer resemblance in other important parts of the 

 skeleton. 



The stylo-hyal bone is hammer-shaped in the Sloths as in the Megatherioids, 

 but the handle is relatively shorter, which agrees with the shorter cranium ; that 

 of the Cholwpus comes nearest the Megatherioid type of the bone in the form of 

 its expanded extremity, which in the Bradypus proper, or three-toed Sloth, sends 

 up a longer and more slender articular part at an acute angle with the shaft of 

 the bone. 



In the Armadillos, at least in Dasypus sexcinctus, the stylo-hyal is relatively 

 much shorter and more simple than in the Sloths or Megatherioids, and the 

 cerato-hyal is joined with the body of the hyoid by a separate small ossicle. The 

 posterior cornua are however anchylosed to the body, but this is characterized 

 by a pair of processes at its under part. In the Orycteropus the body of the 

 hyoid is relatively broader than in the Megatherioids or Sloths, and both the 

 anterior and posterior cornua are moveably articulated with it : the stylo-hyoid 

 is as short and simple as in the Armadillos. The hyoid apparatus in the true 

 Ant-eaters {Myrmecophaga) and Pangolins {Manis) deviates still further, as their 

 anomalously-proportioned tongue may well render probable, from the type of 

 that part in the Sloths and Megatherioids ; and further comparisons with the 

 hyoidean apparatus in quadrupeds not of the Edentate order would throw no 

 additional hght on the immediate subject of the present memoir, viz. the osteo- 

 logy and affinities of the Mylodon. 



Description of the Vertebral Column. 



The central axis of the skeleton of the Mylodon presents a character of great 

 strength in relation to the size of the animal ; but derives its most striking 

 feature from the anchylosis which prevails throughout the pelvic and lumbar 

 regions. 



The true vertebrae are divisible into seven cervical, sixteen dorsal, and three 

 lumbar, yet not more than two-and-twenty are moveable upon each other, the 

 last dorsal and all the lumbar vertebrae contributing to form an anterior pro- 

 longation of a peculiarly extensive sacrum. The cervical vertebrae are short, 



