THE RODENTS 



193 



I j, c£,P7,M-|.total20. 



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Both cheek teeth and palate show greater specialization than 

 in the foregoing representatives of the order. The palate is 

 narrow and terminates at the level of the interval between the 

 second and third molars. The incisors are somewhat com- 

 pressed and the premolar in each jaw is completely molariform. 

 The complexity of the molars is not so baffling as at first ap- 



Fig. 69. — Dentition of Brazilian Tree Porcupine (Coendou prehensilis, 9.3213-2). In 

 spite of the growing complexity of the crown pattern in the cheek teeth there are not 

 yet persistently growing or fully curved roots as in the following example (Fig. 70). 



pears to be the case. As in the Kangaroos the two inner cusps 

 (protocone and hypocone) in the upper molars and the two 

 outer cusps (protoconid and hypoconid) in the lower teeth 

 are connected by antero-posterior ridges. In both jaws these 

 two cusps can thus be distinguished. The upper molars present 

 anterior and posterior cingula both proceeding laterally, the 

 former from the protocone, the latter from the hypocone; 

 separated from these and from each other by deep grooves are 

 the ridges running to the paracone and the metacone respec- 



