230 



"The internal malleolus is very slightly produced in any Marsupial"*, save in the 

 Wombat and Kangaroo. 



"The fibula is complete and forms the external malleolus in all Marsupials ;" and such 

 may be inferred to be its condition from the evidences of attachment shown in the tibia 

 of Diprotodon. Only, instead of "the close contact and attachment ensuring a due de- 

 gree of fixity and strength"* in the Kangaroos, I infer from the articular surfaces on 

 the tibia for the fibula and for the foot that this "enjoyed a movement of rotation 

 analogous to the formation and supination of the hand"*, as in all save the saltatory 

 Marsupials ; and we may infer a corresponding modification of the foot approximating 

 Diprotodon to Phascolomys. 



§ 11. Conclusion. — Thus in the series of Mammalia which characterizes the Austra- 

 lian continent we have evidence of the former existence of a species as large as the 

 Megatherium — that strange extinct animal which similarly crowns the series of Bruta 

 correspondingly characteristic of the South American Continent. 



It is interesting to note the similarity in size, number, and form of working-surface of 

 the molar teeth in the extinct Marsupial and Bradypodal giants ; so much so that, not- 

 withstanding the different dental structures and conditions of growth, one cannot resist 

 the inference of a correspondence of diet. But whereas in Megatherium the front teeth 

 arc wanting, and the prehension of the vegetable food was allotted to limbs and tongue, 

 in Diprotodon instruments allied to those by which the Beaver and Wombat gnaw the 

 ligneous fibre were magnified to the proportions of the body to be provided for. The 

 Marsupial monster brought down the tempting foliage by erosion of the trunk, not by 

 the strong hawl of a forcible grasp. Accordingly, the limbs show not those abnormal 

 proportions which distinguish the Megatherioids ; they manifest, especially the hind 

 ones with the pelvis, in the Diprotodon, forms and proportions recalling those of the 

 Elephant, and suggestive of analogous uses and mode of progression. The fore limbs 

 may be inferred by the modifications of the distal articulation of the humerus, and by 

 what is known of the ulna, to have enjoyed the rotatory as well as flexile movements. 

 Herein the Diprotodon resembles the Megatherium rather than the Elephant ; but the 

 truer inference from the retention of the rotatory and probably unguiculate structure of 

 the fore paws is that, as in the existing herbivorous Marsupials, they were needed for the 

 manipulations of the pouch. 



The resemblance in the Diprotodont and Megatherioid dentitions, guiding to the re- 

 cognition of function or adaptive purpose, are underlain, as above hinted, by differences 

 of textural and genetic conditions. Diprotodon combines enamel with dentine, osteo- 

 dentin, and cement ; Megatherium has no enamel. In Diprotodon the molars have a 

 limited period of growth ; in Megatherium that period was limited only with life. 



The Australian giant adds to number, relative size, and shape of crown, of its molars, 

 m which it accords with the existing macropodal marsupial dwarf of that land, the 

 further correspondence in the coronal enamel and the divergent roots of the grinders. 



* Osteology of the Marsupialia, he. cit. p. 405. 



