TEETH OF MAMMALS. 
21 
the typical condition, which, as will be seen, is very nearly 
preserved in the human hand. One series shows some of 
the stages of modification for special purpose (specialization) by 
which a typical five-fingered hand becomes converted into 
that of the single-fingered Horse, and another series ends with 
the hand of the ruminants, with only two fingers remaining, some- 
times, but erroneously, called a " cloven hoof." ■ Similar changes 
are shown in the toes of the hinder extremity, illustrating the 
same common plan running through infinite modifications in 
detail, enabling the organ to perform such a variety of purposes, 
and to exhibit such diversity of outward appearance. The 
existence of this common plan is now generally regarded as 
due to inheritance from a common ancestor. 
The central case of the bay contains a collection illustrat- 
1 T Mammals. 
mg the principal characters of the teeth m the Mammalia. 
Its inspection should commence at the north-east corner, where 
the visitor will find himself after completing the survey of the 
osteological specimens in the wall-cases. In the first division 
specimens are placed showing the general characters of 
teeth, their form, the different tissues of which they are 
composed, the two great types of dentition in mammals, 
homodont and hetcrodont the nomenclature and homologies of the 
different teeth, and their development and succession. The 
principal modifications of teeth according to function are next 
shown by examples of forms adapted for fish-eating, flesh- 
eating, insect-eating, grass-eating, &c. The remainder of 
the case is taken up by examples of the dentition of the 
different families of mammals arranged in systematic order, 
prepared so as to display not only the shape of the crowns, but 
also the number and character of the roots by which they are 
implanted. 
In bay No. II. the two wall-cases contain a collection arranged Bay II. 
to show in a synoptical manner the generally recognised of^;^j^als^ 
orders and sub-orders of existing Mammals, by examples 
selected to illustrate the predominating characters by which 
tliese are distinguished. A brief popular account of the 
characteristics of the group, and a map showing its geographical 
distribution, is placed with each. This is intended not only for 
an introduction to the study of the class l)y visitors to the 
