1896.] MAMMALIAN DENTITION. 577 



suocessional teeth, shows conclusively to my mind that the first 

 premolar is present as a calcified tooth in one dentition only, viz., 



in the milk-dentilion ; the milk-tootli (^^^i) being very large and 

 persisting in the adult along with the permanent teeth, a slight 

 trace only of its successor being visible at a very early stage and 

 only for a short period. 



i must further conclude that the teeth figured by Bate as 



c pm. j^^^^ ^^^ existence, his REEii-,^ being in reality persistent milk- 



dpm. 1 ppm. 1 ° 



teeth. 



I can only imagine that Bate was misled by the presence of the 

 small needle-like teeth seen in connection with all the other ante- 

 molars into the belief that he had lost a similar one in connection 



with 5^^^ during dissection. 



Leche, while accepting Bate's account, which he was bound to 

 do from the limited material at his disposal, states that pm. 1 was 

 much more backward than the other milk-teeth, for while the 

 latter had well differentiated enamel-organs, that belonging to 

 pm. 1 was still club-shaped or only slightly advanced. Thus his 

 specimens form with mine a perfect series, which together show 

 that at uo time is there more than one representative of pm. 1 

 differentiated as a tooth, i. e. dpm. 1, and only for a short period is 

 there any indication of ppm. 1. 



General Comideration of the Homology o/Pra. 1. 



Although there is undoubtedly but one calcified representative 

 of pm. 1 present in the Mole, it is possible that some may be 

 inclined to regard that tooth as belonging to the permanent rather 

 than to the milk series ; in that case the lingual growth of the 

 dental lamina would have to be regarded as the representative of 

 the post-permanent series, similar to that seen in connection with 

 the permanent incisors and canines (fig. 28, jjc. dl.). Such an 

 interpretation has been adopted by Tims (24) for pm. 1 of the Dog 

 and Pig', this author further stating his belief that in those cases 

 (Hyrax, &c.) in which pm. 1 is duplicated, the two teeth repre- 

 sent the permanent and post-permanent series, and not the milk 

 and permanent sets as one might suppose them to do. Against 

 this possible interpretation of pm. 1 in the Mole may be urged in 



' With regard to Time's description of tbe 1st premolar of the Pig, in which 

 he figures traces of three dentitions, I believe that there has been a mistake in the 

 identification of the teeth, for which I am partially responsible, the sections and 

 rough identification of tbe teetb being mine. On nialclng n fresh and more care- 

 ful examination of tbe sections, and comparing them with an older specimen, 

 I find n very backward tootb-genn present between the canine and tbe supposed 

 1st premolar: this backward germ I take to be tlio true pm. 1, the tooth 

 figured by Tims being dpm. 2 ; in that case the enormous development and 

 swollen nature of the lingual growth of the dental lamina is accounted for, it 

 being the germ of ppm. iJ, while the labial growth must represent a trace of the 

 pre-milk dentition. 



