122 FAMILIAR TALK CONCERNING THE TEETH. 



which answers to the little finger of the human hand, there is only a rudi- 

 ment. This is, however, as far as European deposits have been enabled to 

 carry us with any degree of certainty in the history of the horse. In the 

 American tertiaries, on the contrary, the series of equine forms is continued 

 down to the bottom of the Eocene. The older Miocene form, termed Meso- 

 Mppus, has three toes in front and a large splint-like rudiment representing 

 the little finger, and three toes behind. The radius and ulna are entire, 

 and the tibia and fibula distinct, and the teeth are anchitheroid with short 

 crowns. 



"But the most important discovery of all is the Orohippus — which comes 

 from the lower part of the Eocene formation, and is the oldest member of 

 the equine series known. Here we have four complete toes on the front- 

 limb, three toes on the hind-limb, a well-developed ulna, a well-developed 

 fibula, and the teeth of simple pattern. So you are able, thanks to these 

 great researches, to show that, so far as present knowledge extends, the 

 history of the horse-type is exactly and precisely that which could have 

 been predicted from a knowledge .of the principles of evolution. And the 

 knowledge we now possess justifies us completely in the anticipation that 

 when the still lower Eocene deposits and those which belong to the Creta- 

 ceous epoch have yielded up their remains of equine animals, we shall find 

 first an equine creature with four complete toes and a rudiment of the in- 

 nermost toe in front, and probably a rudiment of the fifth toe in the hind- 

 foot. (Since this lecture was delivered, Prof. Marsh has discovered in the 

 lowest Eocene deposits of the West a new genus of equine mammals (^Eohip- 

 2nis), which corresponds very nearly to this descri^Jtion. — American Journal 

 of Science, November, 1876.) In still older forms the series of the digits 

 will be more and more complete, until we come to the five-toed animals, in 

 which most assuredly the whole series took its origin. 



"That is what I mean, ladies and gentlemen, by demonstrative evidence 

 of evolution. An inductive hypothesis is said to be demonstrated when the 

 facts are shown to be in entire accordance with it. If that is not scientific 

 proof, there are no inductive conclusions which can be said to be scientific. 

 And the doctrine of evolution at the present time rests upon exactly as se- 

 cure a foundation as the Oopernican theory of the motions of the heavenly 

 bodies. Its basis is precisely of the same character — the coincidence of the 

 observed facts with theoretical requirements." 



FAMILIAR TALK CONCERNING THE TEETH. 



I have so many times been asked by my patients why it is possible for a 

 tooth to ache after the nerve has been killed that I propose to try to explain 

 to the readers of the Journal, in as simple a manner as possible, avoiding 

 -all technicalities, why such a seeming contfadiction can occur. If a longi- 

 tudinal section be made of a tooth, a cavity nearly corresponding in shape 



