324 THROUGH THE HEART OF PATAGONIA 



to the fragments of stem, their affinities are altogether doubtful. There 

 are numerous silicious particles in the excrement, and there are many 

 pieces of the underground parts of the plants, suggesting that they have 

 been pulled out of the ground. A few pieces of stems are sharply cut, 

 not bruised or torn at the end." The latter fact is especially important 

 in connection with Dr. Hauthal's discovery of cut hay in the cavern, 

 and his theory that the Gtypotherium was kept in captivity and fed 

 by nnan. 



Generic and Specific Determination. 



The fortunate discovery of all parts of the skull and dentition renders 

 the generic determination of this Ground-Sloth now quite certain. The 

 teeth show that it belongs to the family Mylodontidse ; the presence 

 of onlyfour instead of five upper molars separates it from the genera 

 Mylodon, Lestodon, and Scelidotherium ; the forward production of the 

 nasals and the ossification of part of the internarial septum place it 

 definitely in the allied genus Grypotherium, as originally diagnosed by 

 Reinhardt. The only question needing consideration is, whether the frag- 

 ment of cranium described by Owen in 1840 as the type of the genus 

 Glossotherium* is really identical with that subsequently described by 

 Reinhardt under the name of Grypotherium darwini, as now seems to be 

 commonly believed. 



Darwin's original specimen, on which the genus Glossotherium of Owen 

 was founded, is preserved in the Museum of the Royal College of Surgeons. 

 It has thus been possible to compare it directly with the undoubted 

 cranium of Grypotherium from the Patagonian cavern. The specimen is 

 merely the left half of the hinder part of the cranium, and is therefore very 

 inadequate for discussion ; but several features seem worthy of note. Com- 

 pared with the new skull No. i, the fragment named Glossotherium has 

 (i.) the inner wall of the temporal fossa less flattened, (ii.) the digastric 

 fossa deeper in proportion to its width, (iii.) the hinder border of the in- 

 flated pterygoid vertical, instead of sloping downwards and forwards, (iv.) a 

 much larger and deeper pit for the articulation of the stylohyal, and (v.) a 

 longer canal penetrating the base of the occipital condyle for the passage 

 of the hypoglossal nerve. In all these respects the so-called Glossotherium 

 agrees .much more closely with the typical Mylodon ; and Owen was pro- 

 bably correct in 1842 when he expressed the opinion that the two are at 

 least generically identical.! 



* R. Owen, "The Zoology of the Voyage of H.M.S. Beagle.— Va.ri I. Fossil Mam- 

 malia" (1840), p. 57, pi. xvi. 



t R. Owen, " Description of the Skeleton of an Extinct Gigantic Sloth, Mylodon 

 robustus, Owen" (1842), p. 154, foot-note. 



