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 series 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 Euminants, 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 fix»m 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 comer, 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, 

 homosodont 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 homceodont type the teeth are alike, in the heterodont they arc 

 divided iuto groups. 



