112 MICROSCOPIC ANATOMY OF THE TEETH 



above named says, the enamel of Pteromys (flying squirrel) 

 and Spermophilus (the American Souslik) may be recog- 

 nized at first sight as belonging to the Sciuridse. 



Hystri- In the Porcupine (Hystrix), although the portion of enamel 

 near the dentine is laminated as in other Rodents, the 

 structure is much complicated by the flexuous course of the 

 prisms. The laminae which leave the dentine at an angle of 

 80 become confluent, and, as Sir John Tomes says, the 

 enamel prisms appear as if thrown into waves, ' they pursue 



FIG. 62. Enamel of Squirrel (Sciurus). Transverse section. 

 c. Enamel ; d. dentine. ( x 250. ) 



a serpentine course and in the lamelliform portion describe 

 three tolerably uniform curves ', but lie parallel to one another 

 in the outer portion of the enamel as in other Rodents. 



The enamel of the Capybara (Hydrochoerus) is very 

 similar in structure to that of the Porcupine, but the 

 lamellae of the inner layer are more confluent and more 

 parallel. The enamel near the dentine is crowded with 

 small rounded spaces. 



The enamel of the Marmots (Arctomys) differs from that 

 of the Sciuridse, but is not wholly different in type. The 

 prisms in the first part of their course are seen in longitudinal 

 sections to lie in parallel layers at right angles to the dentine, 



