APPENDIX A 321 



Auditory Ossicles. 



The auditory ossicles were preserved in the tympanic cavities of both 

 skulls, Nos. I and 2, being retained by the dried soft parts. They were 

 detected by Prof Charles Stewart, who kindly extracted them, with great 

 skill, from both sides of each skull. Comparing these ossicles with the fine 

 collection in the Royal College of Surgeons, they prove to be closely similar 

 to those of all the existing Sloths, but most nearly resembling those of 

 Cholxpus didactylus. The malleus is bent exactly as in the latter species, 

 and is of similar shape. As observed by Prof Stewart, it is remarkable 

 in articulating with the incus not only by the head, but also by a diminutive 

 lower facet, which is in contact with a small facetted process on the 

 anterior arm of the incus. A feeble indication of the same secondary 

 articulation is also observable in Choloepus ; but it is curiously absent in 

 the second specimen of Grypotherium. The two divergent arms of the 

 incus are equal in length, as usual in the Sloths. The stapes is only 

 very slightly perforated in both specimens ; while a small circular disc 

 firmly fixed to the incus represents the orbicular bone in the second skull. 

 The auditory ossicles of Grypotherium, therefore, are very different from 

 those of Myrmecophaga, in which the malleus is less sharply bent, the 

 incus has divergent arms of unequal length, and the stapes exhibits a large 

 perforation.* 



Vertebra and Limb-bones. 



Nearly all the remains of vertebrae and limb-bones are in the same 

 state of preservation as the portions of skull and mandible already 

 described, with adherent cartilage and traces of muscles and ligaments. 

 With some of the ungual phalanges there are also well-preserved examples 

 of the epidermal sheath. As already remarked by Roth, the edges of 

 one sheath probably belonging to the fourth digit of the manus, are 

 quite sharp, and indicate that if the animal walked on its fore feet it 

 resembled Myrmecophaga in the peculiar twist of the manus. 



All the specimens in this series seem to have been accurately deter- 

 ,mined and sufficiently described by Roth. It is only necessary to 

 emphasise the fact that the two shafts of humerus with abraded, not 

 sharply broken, ends have a much more fossilised appearance than any 

 •other specimen in the collection, and are deeply stained throughout by 

 ferruginous matter. The small shaft. No. 22, certainly seems to have 

 belonged to an adult animal,. as remarked by Roth, and it was probably 

 much smaller than any individual indicated by the other remains. 



' * J. Hyrtl, " Vergleichendanatomische Untersuchungen iiber das innere Geharorgan 

 des Menschen und der Saugethiere " (1845), p. 135, pi. v. Fig. 6. 



