17 



The capacious trunk, thus slightly elevated upon its short and strong sup- 

 porters, presents the form of a cone, gradually tapering forwards from the 

 enormous pelvis which forms its hase, to the short neck and slender head. 



For such proportions and combinations we may search in vain amongst the 

 skeletons of existing Mammalia ; but the palaeontologist will recognise them in 

 the Megatherium. The precise nature and amount of the affinities of the 

 Mylodon to this and other extinct Edentata, and to the existing species of that 

 order, will be deduced from the following more detailed description. 



Description of the Skull. 



The small relative size of the skull of the Mylodon robustus, and its short, 

 broad, and abruptly truncated muzzle, have been already alluded to. Progress- 

 ive ossification has obliterated most of the sutures, and has reduced the origin- 

 ally complex assemblage of bones forming the cranium and upper jaw to an 

 almost continuous whole : this will be first described as seen from the lateral, 

 the superior, and inferior aspects : the shape and connections of the constituent 

 bones will next be given, so far as they can be satisfactorily traced. 



Side-view*. — The skull of the Mylodon robustus presents, from this aspect, 

 the form of an elongated parallelogram, chiefly characterized by the singular 

 form and development of the malar bone, and by the shortness and depth of the 

 muzzle. 



The occipital plane, bounded behind and below by the large condyles, inclines 

 forwards as it rises to join the upper surface of the cranium. This surface ex- 

 tends horizontally in a nearly straight line to the muzzle, being slightly de- 

 pressed at the root of the nose, and gently convex in the rest of its extent. 



The maxillary part of the cranium terminates suddenly by a vertical concave 

 line, and, independently of the lower jaw, is deeper than the opposite or occipital 

 termination: the cranium, in fact, contrary to its usual proportions, gradually 

 increases in depth as it extends forwards ; and, as the lower jaw diminishes in depth 

 in the same direction and degree, the base of this bone taken as that of the entire 

 skull, runs parallel, when the mouth is closed, with the coronal line of the skull. 



The side of the cranium is bounded, posteriorly, by a prominent but flattened 



• Plate II. 



