ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
23 
of the lower Eocene the primitive anterior portion (trigonid) of the 
crown was reduced to the level of the posterior portion (talonid) while 
retaining all its cusps. The oldest monkey or Lemur known — Anapto- 
morphus — illustrates the loss of the antero-internal cusp or paraconid. 
This accounts for the history of all the cusps in the human lower molar. 
“ Thus, in the rich series of Mesozoic and lower Eocene mammals we 
can observe the actual rise, succession, and decline of all the six cusps, 
and do not require any new hypothesis to explain their appearance.” 
Rudiments of Teeth in Manis.* — Dr. 0. Rose has found, in study- 
ing Prof. Max Weber’s preparations of Manis embryos, a dental ridge 
(. Zahnleiste ) in the upper jaw, and even rudiments of teeth in the lower 
jaw. These rudiments are represented by a club-shaped swelling of the 
dental ridge and soon disappear. 
Dentition of Marsupials.! — Dr. C. Rose maintains that the develop- 
ment of the teeth in Marsupials is essentially like that in other Mammals. 
The first stage is a ridge of epithelium which grows into the mesoderm. 
On this appear the rudiments of the first set. In Didelphys these are 
the incisors, the canine, two premolars, and the first molar. These 
are constricted off from the ridge which grows inwards and backwards. 
The posterior molars arise, as Rose has described in man, by the lateral 
extension of the dental ridge. But while in man the supplementary 
ridge forms as many replacement teeth as there are of the first set, from 
that of Marsupials there usually arises only the last premolar. It is 
more than likely, however, that the last incisors of Perameles, Macropus, 
and Phalangista are formed from the replacement ridge, i. e. belong to 
the second set. The last premolar may slip into a gap in the first series 
(Didelphys, Perameles Doreganus, Belideus hidens , Phalangista Gookii, 
and Myrmecobius), or it may replace the last premolar of the first set 
(. Phalangista , Macropus lugens, M. giganteus, &c.). With the exception, 
then, of the last premolar, and possibly of the last upper incisor of 
some species, the teeth of Marsupials correspond to permanent milk- 
teeth. In the reduction of dental replacement the Marsupials seem 
almost to have overshot the mark. “ Sie haben sich in eine Sackgasse 
verirrt, aus der kein Ruckweg moglich ist.” 
Rose seeks to confirm his theory that premolars and molars arise from 
the fusion of several simple teeth. In the extinct Triacanthodon the 
premolars are quite like the molars ; the inferior premolar of Macropus 
lugens is still triconodont, the upper one is in transition to the trituber- 
cular type ; in M. giganteus the premolars are tritubercular ; and so on. 
Dental Ridge and “Egg-teeth” in Sauropsida.if — Dr. C. Rose 
finds in embryos of Sterna Wilsoni a distinct dental ridge ( Zahnleiste ), 
but no dental rudiments. A slight hint of papillae is due to a folding 
of the horny epithelium as the beak becomes curved ; and probably this 
is true also of the well-known papillae of certain parrots. In Chelone 
Midas the dental ridge was again found, but nothing more. The true 
“ egg-tooth ” found in reptiles with parchment-like egg-shells is a den- 
tine tooth situated on the premaxilla, and is quite distinct from the knob 
* Anat. Anzeig., vii. (1892) pp. 618-22 (4 figs.). 
f Tom. cit., pp. 639-50, 693-707 (23 figs.). 
X Tom. cit., pp. 748-58 (14 figs.). 
