TEETH OF MAMMALS. 
23 
of the structure of bone and cartilage as shown by the micro- 
scope. 
In the wall-case on the opposite (north) side of the bay the 
outline of the osteology of Mammals is continued by illustrations 
of the structure of the limbs. At the top of the case is a 
diagram showing the correspondence of the hand and the foot 
in their complete typical form, with the names applied by 
anatomists to the different bones. The semes of specimens 
below shows the principal deviations actually occurring from 
the typical condition, which, as may 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 the 
single-toed fore- foot of the Horse, and another series ends with the 
fore-foot of the Kuminants, with only two toes remaining, some- 
times, but erroneously, called a " cloven hoof" Similar changes 
are shown in the toes of the hind-foot, 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- Teeth of 
ing the principal characters of the teeth of Mammals. ■'^^"^"^^^ 
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 
are placed specimens showing the general characters of 
teeth, their form, the different tissues of which they are 
composed, the two great types of dentition in Mammals, 
homoeodont and heterodont* the names and serial correspondence 
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 
families of Mammals arranged in order, and prepared so as 
* In the homoeodont type the teeth are alike, in the heterodont they arc 
divided into groups. 
