532 ZOOLOGY SECT. 



The canine is very small and early lost. Of the polyprotodont 

 forms (Fig. 1120) the Australian Dasyure or Native Cat has the 

 formula 



.4 1 24 



and the American Opossum (Didelphys) (Fig. 1121) 

 .513 4 



*4>M'*'3; m '4 = 



The Edentata, as noticed in the outline of the classification, 

 though not by any means all toothless, always have some defect 

 in the dentition ; when teeth are present in the adult the anterior 

 series are absent and the teeth are imperfect, wanting roots and 

 often devoid of enamel. The tooth-characters differ widely in the 

 different groups. In the Sloths there are five teeth above and 

 four below on each side ; no second series is known. In the 

 American Anteaters there are no teeth in the adult. In the 

 Armadillos, on the other hand, the teeth are numerous, though 

 simple and rootless, and in one genus at least two scries occur. 

 In the Scaly Anteaters there are no teeth. In the Cape Ant- 

 eaters (Fig. 1122) again there are numerous teeth which are 

 heterodont and diphyodont and have a peculiar structure, being 

 perforated by numerous minute parallel vertical canals ; the pulp 



FIG. 1122. Section of lower jaw and teeth of Orycteropus. (After Owen.) 



of each tooth, entire at its base, is divided distally into a number 

 of parallel columns. 



In the Ungulata the dentition is heterodont and diphyodont, and 

 the teeth are very rarely devoid of roots. In the Artiodactyla the 

 premolars and molars differ from one another in pattern ; the 

 first upper pre-molar is almost always without a milk predecessor. 

 The Pigs (Fig. 1123) are among the very few recent Mammalia 

 which possess what has been referred to as a typical dentition : the 

 formula of the completed dentition is 



.3143 



*' 3' C ' 1' P ' 4' m ' 3 = 



