32 Bulletin American Museum of Natural History [Vol. XL VII 



above the gum to full maturity of the permanent set. Several stages of 

 development are also shown in the accompanying text figure (Stages 

 1-8). 



Deciduous Dentition 



The milk dentition, strictly construed, consists of 24 teeth: 1^, 

 Cfzi, P|zf = ^ = 24. The first premolar (p ~) is not present till later 

 and has no successor. 



Upper or Maxillary Series. — The single upper incisor (i 3 by 

 position) is a minute spicule inserted at the extreme posterior border of 

 the premaxilla and has no successor. Although small and frail, it often 

 persists through life, being frequently present in the senile stage. In 46 

 adult skulls, taken at random for the investigation of this point, 15 (33 

 per cent) were found to retain one or both upper incisors, both being 

 present in 6 skulls and one in each of 9 skulls, most frequently on the 

 right side. When these teeth are absent their alveoli often remain, 

 indicating the recent presence of the teeth. 



The canine is a small bicuspid tooth, with a slender-pointed central 

 cusp, and a small slender-pointed posterior cusp, about one-third as 

 high as the main cusp. The canine is shed at the same time as the pre- 

 molars, but its successor is long in maturing, and, when fully developed, 

 is long, slender, and saber-like. The second, third, and fourth premolars 

 (dp 2 , dp 3 , dp 4 ) arise simultaneously. Dp 2 has a basal length slightly 

 exceeding its height, with two pointed cusps, the anterior one consider- 

 ably exceeding the other in size and height, and a low anterior and a low 

 posterior cusplet, both arising from the cingulum. Dp 3 is sub triangular 

 in basal outline, the anterior half narrow, the posterior broad, with a 

 main central cusp, a smaller one behind it, and a still smaller one in 

 front, on the cingulum. There is also a low, broad postero-internal cusp, 

 and, behind this, a slight cusplet from the cingulum. Of these five cusps, 

 three are external and two internal. Dp 4 is subquadrate and distinctly 

 molariform, with four prominent cusps, the outer much higher than the 

 inner, the four cusps collectively enclosing two deep basin-shaped 

 cavities. There is also an anterior cusplet from the cingulum. 



Lower or Mandibular Series. — The anterior four milk teeth in 

 the lower jaw are all incisiform, similar in size and general form, and have 

 their axes directed forward. The two middle teeth are tricuspid, the 

 first and fourth bicuspid. They are separated from dp 2 by a long convex 

 diastema. The first three incisiform teeth are shed singly at intervals. 

 The three posterior milk premolars (dp 2 , dp 3 , dp 4 ) increase successively 



