a MAESTJPIALIA. 



having vacuities between the posterior molars. The alisphenoids 

 are large, and form the auditory hullse should these be developed ; 

 while the tympanies are small, annular, or tubular, and but rarely 

 fused with the other bones of the skull. Finally, the mandible, 

 except in Tarsipes, has its angle more or less inflected, although 

 some Marsupials have this character less developed than certain of 

 the Insectivora. 



The teeth are exceedingly variable in structure, being modified 

 either for a graminivorous, frugivorous, insectivorous, or carnivo- 

 rous mode of life. Their number is, normally, as follows : — 



1. 1^^, C. I, P. I, M. i X 2=40 to 50, 



but the total number sometimes descends to 22 (Tarsipes), while it 

 amounts to 52 in Myrmecobius. 



The division of the seven cheek-teeth ordinarily present into 

 three premolars and four molars is very charaoteristic of the Order, 

 as compared to the four premolars and three molars of the typical 

 placental Mammals. 



The tooth-change is always confined to a single tooth, the last of 

 the premolars (p."), which alone has a milk-predecessor ; and in 

 some cases even this milk-tooth is rudimentary or altogether 

 aborted. 



Synopsis of the Families. 



I. EXIEHNAL ChARACTEEB. 



. (Diprotodont.) Hind feet syndactylous. 



Vegetable-feeding*. -^ 

 a. Tail long t ; ears well developed, 

 a'. Hind limbs much larger than forej. 



No hallux § I. MacropodidsB.'p. 3. 



b^. Limbs subequal. A large oppo- ' [p. 126. 



sable hallux II. Phalangeridae, 



h. Tail and ears rudimentary III. Phascolomyidae, 



. (Polyprotodont.) Animal-feeding*. . [p. 212. 



c. Hind feet syndactylous. Hallux 



minute or absent IV. PeramelidsB, 



d. Hind feet not syndactylous. [p. 219, 

 c\ Hallux not opposable. Tail not 



prehensile V. Dasyuridffi, p. 253. 



tZ'. Hallux opposable. Tail generally 



prehensile VI. Didelphyidse, 



[p. 315. 



* With a few unimportant exceptions, 

 t Except Fhasiolarctm. 

 \ Except Dendrolagus and Hypsiprymnodon. 

 § Except Hypsiprymnodmi. 



