629 



The presence of the continuations of the distal end of the dental 

 lamina and their situation on the lingual side of the molars, at any 



■<_ Bös 



Fig. 3. Transverse section ,>.--"•,: '0>'"' a "'''; f^^&J ' 



through the first lower molar of l If' ■' /■>;.' i ^uv£&^'-, v '"'!•%-■"" v ;lL ,. 



a Guinea Pig at a stage in which 



mm 



two molars were well developed. ' ; !,•-• ' ' '!&f/i&~': PY": ' > .v-7..-" 1 . / ';~' ' - 02 ' 



X 40. to, functional molar, e 



lingual downgrowth of dental 

 lamina (rudimentary second set). 



m. 



rate in the case of the 1st molars of the Guinea Pig, would suggest 

 that they represented the undeveloped rudiments of the successional 

 teeth and that the molars themselves are to be refered to the first 

 dentition. Iresh par. As mentioned previously Kükenthal has sug- 

 gested that there are traces of at least 3 dentitions in the young 

 Mammalia, while Leche goes further and asserts the presence of 

 traces of 4 sets of teeth. 



The former figures a section of a seals molar which shows 

 what he believes to be traces both of an earlier and a later dentition 

 in addition to the functional tooth. If this figure be compared with 

 those published by myself (1. c. PL XXXVII, figs. 25 a and 6, and 26) 

 of the Macropid molar, it will be seen that the labially situated 

 downgrowth of the dental lamina which he figures for the seal evi- 

 dently corresponds with the more largely developed one which I dis- 

 covered in Macropus, my specimen being however much younger did 

 not show any trace of a dentition later than the functional molars 

 and at present I cannot state definitely as to the existence or not of 

 such a structure. I concluded at the time from the material at my 

 disposal that the labial growth of the dental lamina represented the 

 milk dentition and the functional tooth the permanent one (2nd and 

 3rd). When I drew these conclusions we had not sufficient evidence 

 in our possession to justify the idea that there were more than two 



cessional tooth, as the second molar itself often develops in this position 

 owing to the shortness of the jaw of the foetus. 



