594 



PROF. F. AVOOD JONES ON THE 



holes in the jaw-margin, and the tooth itself is not to any extent 

 received in a depressed area of the jaw. 



The anterior molar has 5 roots, a large single median anterior 

 root and 4 others arranged in pairs behind it. 



The second molar has 4 roots arranged as an anterior pair and 

 a posterior pair. The third molar has an anterior pair of roots 

 arranged labio-lingually and a single median posterior root. In 

 the whole root series there is a single anterior median root, and a 

 single posterior median root, and 5 lingual and 5 labial roots 

 arranged in pairs (see text-fig. 6, B). 



What might be termed the root-formula for the upper molai"s 

 would therefore be 5. 4. 3. 



Lower Molars. 



The occlusal surface of the lower molars shows two sub-divisions 

 of the crown of the two posterior molars and three sub-divisions 

 of the anterior molar,, the anterior and middle sub-divisions of 

 the anterior tooth being often partially fused together (see text- 

 fig. 7, A). 



The root-cavities are vs^ell developed and clear cut, like those of 

 the upper molars. The anterior tooth has 4 roots, consisting 



Text-fissure 7. 



Left lower molar series of JRattus greyi. A, the occlusal surface; 

 and B, the alveolar cavities. 



of an anterior median rounded root followed by a pair of roots 

 (lingual and labial), followed again by a single root elongated 

 from side to side. 



The second and third teeth have 3 roots each arranged as a 

 pair of anterior rounded roots and a single elongated posterior 

 root (see text-fig. 7, B). The lower root-formula could therefore 

 be written as 4. 3. 3. 



(2) R. terrce-reginoi shows exactly the same condition as R. greyi 



