192 



MAMMALIAN DENTITION 



if.cf.p^Mf.totane. 



This dentition is more specialized than that of the Sciuro- 

 morpha since the milk teeth never appear and the typical 

 mammalian pattern of the molars is more obscured. The Rat 

 is an omnivorous feeder and its brachyodont and bunodont 

 molars are tuberculated in a fashion somewhat similar to those 



Fig. 68.— Dentition of Brown Rat (Mus norvegicus, 9.3212-2). Note the tuberculated 

 swine-like features of the cheek teeth. 



of the Pig. The parallel rows of cheek teeth, the retention of 

 a small third molar and the formation of the palate are rela- 

 tively unspecialized features. The first molar in this animal 

 on the other hand is considerably enlarged. 



We pass next to the Hystricomorpha and take for our ex- 

 ample Coendou prehensilis, the Tree Porcupine of Brazil (Fig. 

 69). This arboreal animal feeds upon the leaves, young shoots 

 and bark of the trees in which it lives. The tooth formula is: 



