1896.] MAMMALIAN DENTITION. 567 



PPm-2 , and fig. 14, p pt"-3 ). The upper c1p"'-2 is larger thati dpiij.2, 

 possibly at times it cuts the gum ; it is well seen in a specimen in 

 the IBritish Museum (fig. 13, dpm. 2), probably the one Thomas 

 described ; no trace of clpm. 2 is seen in that specimen, and it is 

 probable that this tooth is either shed in utero or absorbed. 



' are quite normal, the milk representative being large, and 



the lingual growths of the dental lamina, which give origin to the 

 enamel-organs of their successors, being conspicuously swollen 

 (fig. 14, ppm- 3 ). This tooth is somewhat similar in the t«o 

 dentitions, but distinctly larger in the adult. 



-^ ' -.. — These are the largest and most complex of the pre- 

 molars, and both exhibit conspicuous lingual specializations of the 

 dental lamina, the enamel-germs of their successors. These germs 

 are develo]ied in front of the deciduous teeth, and although the 

 lingually -placed dental lamina is continued back by the side of 

 dpm. 4, it is no longer swollen to form an enamel-germ. 



The Molars. 



In the stnge examined two molars ^^■ere jjresent, above and 

 below, but save in the case of '"■ 1 no labial or lingual developments 

 of the dental lamina were to be seen. M. 1, however, exhibited 

 both a lingual and a slight labial growth, similar to those seen in 

 Erinaceiis. 



The Cusps. 



The molar teeth of Gi/mnvm resemble tlioso of Erinaceus in 

 pattern ; like that genus they exhibit li>'e cusps, which are strongly 

 developed, and in the upper jaw a well-marked cingulum, with a 

 small anterior and posterior cusp, is present in addition ; in the 

 lower jaw the paraconid is less deAeloped than in Erinaceiis. 



My foetal specimen was rather old for an exact determination of 

 the cusp ontogeny, most of the cusps being weU-formed. In "i.l 

 all five cusps were present, and had attained nearly their full 

 development ; the following is their order in size : proto-, meta-, 

 para-, and hypocoues, the smallest being the metaconule. M.2 

 was less developed, and here the para- and metacoues were the 

 most strongly developed, while the protocone was present in the 

 form of a large antero-external shelf, but hardly as yet developed 

 into a distinct cusp, though the hypocone and metaconule had 

 done so. 



Probable order of cusp-development : — 



1. Paracone. 



2. Metacone. 



3. Protocone as a shelf. 



4. Hypocone. 



5. Metaconule. 



6. Protocone as a cusp. 



