517 



Diprotodon. Nototherium. 



Extreme height of neural canal to upper border of hind 



in. 



lines. 



in. 



lines. 



articular surfaces 



2 



o 



i 



6 



Least diameter of postneurapophysial groove .... 







9 



o 



6 



Least diameter of preneurapophysial canal 







4* 



o 



3 



Vertical diameter of interspace for centrum .... 



2 



8 



2 



4 



Transverse diameter of interspace for centrum 



1 



11 



1 



10 



From upper border of occipital cup to that of surface 













A 

 1 



Q 

 O 



i 



X 



« 



Vertical diameter of cup for occipital condyle .... 



3 



4 



2 



11 



Transverse diameter of cup for occipital condyle . . . 



2 



6 



1 



7i 



' 2 





2 



5 



1 



71 

 4 2 



Least fore-and-aft diameter of diapophvsis 



1 



10 



1 









2 



6 



2 



4 











1 



9 



For extremes of variation in the structure of the mammalian atlas, Plate CXXVI. 

 may be compared with the figures of the atlas of Mylodon robustus given in plate vii. 

 of my work on that species *. A like degree of difference pervades the entire osteology 

 and dentition of the gravigrade Sloths as compared with the gravigrade Marsupials. 



PLATE CXXVI. 



Nototherium. 

 Fig. 1. Front view of atlas vertebra, nat. size. 

 Fig. 2. Back view of the same. 



§ 4. Humerus. — This bone in Nototherium (Plate CXXVII.) resembles that of 

 Phascolomys (ib. fig. 7, and Plate CI.) more than that of Macropus (Plate LXIX.). 

 The entotuberosity (Plate CXXVII. c) does not attain, as in Macropus, the level of 

 the articular head (ib. a) of the bone ; but it does not extend ulnad so far beyond the 

 head (a) as in Phascolomys (ib. fig. 7, & Plate CI. figs. 1-4, c). The head is convex, most 

 so in the ancono-thenal direction, and, as in Phascolomys latifrons (ib. fig. 1, a), is bent 

 down in a subangular form upon the anconal aspect of the shaft. The ectotuberosity 

 (Plate CXXVII. b) rises above the head, but in a relatively minor degree than in 

 Phascolomys ; it is continued down the thenal aspect of the shaft into a pectoral pro- 

 cess (ib. fig. 1, e) considerably more developed than in any kind of Wombat; its thick 

 rugous lower and most prominent part gives a quite peculiar feature to the Nototheriau 

 humerus (ib. fig. 3, e'). The uninterrupted continuation of the ridge (e) from the ecto- 

 tuberosity (b) to the pectoral process (e!), dividing the thenal surface of the proximal half 

 of the humerus into the facets f & g, is a character which is more closely repeated in 



* Description of the Skeleton of an Extinct Gigantic Sloth (Mylodon robustus), 4to, 1842. 



