650 



BERTHA E. MARTIN 



In teeth worn with use, it is impossible to determine the number 

 of cusps, but in a young specimen four or five months old the first, 

 second and eighth teeth of the lower jaw are one-cusped, and 

 the others are two-cusped, with a higher lingual and lower labial 

 cusp. In the upper jaw the first and eighth teeth are one-cusped, 

 the others being two-cusped. In each case the eighth tooth is 

 smaller and narrower than the others. 



Fig. 1 Diagram showing teeth in skull a few months after birth, m, maxilla; 

 pm, premaxilla. 



Fig. 2 Camera lucida drawing of germs of sixth front tooth and the seven 

 back teeth in the jaw of an 82 mm. embryo. Ift, last (6th) front tooth; 7bt, sev- 

 enth back tooth. X 15 (reduced |). 



Fig. 3 Camera lucida drawing of lower jaw a few months after birth showing 

 the eight back teeth and the last front tooth which is usually shed at a younger 

 stage. The eighth back tooth {Ibt) had not erupted. Notice the superficial 

 position of the last front tooth. Iht, last (8th) back tooth; Ifl, last front tooth. 

 X 5 (reduced \). 



