44 Order MARSUPIALIA 



2. Teeth 50, upper jaw with 26, lower jaw with 24; each pos- 



terior angle of lower jaw with an inwardly curving 



process, fig. 4-Ob ; nasal bones broadened posteriorly 



Order MARSUPIALIA ; opossum 



Teeth 44 or lels, never more than 22 in either jaw; each 

 posterior angle of lower jaw without an inwardly curving 

 process; nasal bones not broadened posteriorly 3 



3. Canine teeth decidedly larger than adjacent teeth, fig. 117 4 

 Canine teeth either decidedly smaller than incisors or ab- 

 sent, figs. 40c, d, 41 6 



4. Anterior end of skull with a wide, U-shaped notch, fig. 40*; 



length of skull less than 20 mm. (about Y\ in.) 



Order CHIROPTERA ; bats 



Anterior end of skull either without a notch or with only 

 a small angular or narrow notch, figs. 60, 108 ; length of 

 skull more than 20 mm 5 



5. Canine teeth subtriangular in cross section 



Order ARTIODACTYLA ( in part ) ; pig 



Canine teeth rounded in cross section 



Order CARNIVORA ; flesh eaters 



6. Upper jaw having 6 incisors of approximately equal size, 



fig. 40/; length of skull more than 250 mm. (9^4 in.) . . . _ 



Order PERISSODACTYLA ; horse 



Upper jaw having 2 conspicuously large incisors (in some 

 groups followed by minute incisors), fig. 40c, d\ length of 

 skull less than 150 mm. {S% in.) 7 



7. Gap, if present between front teeth and grinding teeth, no 



more than length of a single grinding tooth; canines 



small, fig. 41 Order INSECTIVORA; moles and shrews 



Gap between front teeth and grinding teeth equal to or 

 greater than length of the row of grinding teeth; canines 

 absent, figs. 40c, d, 73d 8 



8. A pair of peglike teeth immediately behind the 2 large in- 



cisors in upper jaw; maxillary region in front of each eye 



socket with bony lattice-work, fig. 40d 



Order LAGOMORPHA ; rabbits 



No peglike teeth behind the 2 large incisors in upper jaw; 



maxillary regions solid bone, fig. 40c 



Order RODENTI A ; rodents 



ORDER MARSUPIALIA 



Marsupials 



The Marsupialia are unique among mammals in that the 

 female gives birth to minute living young and carries them for 

 some time, usually in a pouch of skin (marsupium) or in fur 

 situated on the under side of her body. The marsupials contain 

 both large and small forms, including the famous kangaroos, 

 which mav attain almost the size of a small horse, and the little 



