1896. ] MAMMALIAN DENTITION. 569 
with the fourth tooth, the so-called i. 4, but here the labial enamel- 
organ is more marked and bell-shaped Plate XXV. fig. 18, dc.). The 
gap between the premaxilla and maxilla at this stage is so extensive 
that the germs of several teeth are contained within it, it being 
quite impossible to identify the future boundary line betweeu 
maxillary and premaxillary teeth (fig. 19). But even if it be a 
fact, as Brandt states (1 a), that the four anterior upper teeth are 
situated within the confines of the premaxilla‘, I fail to see that it 
is proven that these teeth are the homologues of the four incisors 
seen in the Polyprotodont Marsupials, but would rather be inclined 
to regard Brandt’s fourth incisor as a canine, abnormally situated ; 
for among the Insectivora this tooth is very variable in its relations 
to the premaxillo-maxillary suture, due probably to the variations 
in relative extension of these two bones, the canine itself remaining 
constant in its position. 
The 2nd and 3rd lower incisors were in a very backward con- 
dition ; both, however, exhibit labial growths of the dental lamina, 
that connected with j.2 being the most marked (fig. 20). The 3rd 
lower incisor is, however, a vanishing structure and does not 
develop into a functional tooth (fig. 21). 
In the upper jaw the tooth which I regard as the anterior 
premolar, usually called the canine (Brandt), was difficult of identi- 
fication, it being hardly differentiated from the dental lamina 
(fig. 19, pm. 2?). 
Of the two undoubted premolars the posterior is the largest and 
the most advanced in development, the enamel-germ of the anterior 
tooth being still in the club-shaped stage, but possessing a well- 
marked cup-shaped labial (fig. 22) enamel-organ belonging to its 
vestigial predecessor. A similar structure to this, but more 
highly differentiated and of still larger size, is attached to the 
posterior premolar (fig. 23, dpm.4), which, from its large size and 
close proximity to the molar teeth, is probably the true 4th pre- 
molar (ppm. 4). 
These three teeth I regard as premolars; in all probability they 
represent pm. 2, 3, & 4. 
* The enamel-organ of the single lower premolar, like ppm. 4, was 
large and highly differentiated (fig. 24) ; it also exhibits the labial 
enamel-organ of its vestigial predecessor. 
The Molar Teeth. 
In the feetus examined by me m.1,m-2 vere distinguishable but 
m. 1, m. 2 ? 
not very advanced in their development ; = exhibited slight 
lingual continuations of the dental lamina. 
1 A reference to Brandt’s figures will show that it is only in Crossopus 
(fig. 2) that the 4 anterior teeth are quite within the limits of the premaxilla; in 
Sorex (fig. 1) the premaxillo-maxillary suture is so represented that the fourth 
toothis situated in the gap between the two bones, a condition characteristic of 
the 4th tooth or canine of many Placentals. 
Provo. Zoot, Soc.—1896, No. XXX VII. 37 
