ORIGIN AND DEVELOPMENT OF THE EXISTING HORSES. 75 



If we attempt to apply these facts to the ancestry of the horse, it is by no 

 means difficult to perceive that gradual change of habitat, causing a correspond- 

 ing change in diet as already indicated, would also compel greater and greater 

 mobility of the mandibular articulation for proper trituration of the new food. The 

 excursions of the lower jaw in these animals have assumed a lateral direction 

 which affords, as I believe, a sufficient explanation for the broadening of the crowns 

 and the lateral flattening of the cusps. The obvious effect of force continually 

 applied in this direction would be to wrinkle the enamel covering of the cusps 

 and ridges, thereby producing the accessory pillars seen in the higher types. By 

 this method, I apprehend, a more and more complex grinding surface has been 

 produced. 



As to the causes of digital reduction, I have already assigned a primary 

 reason. Prof. Cope has shown,* that in plantigrade quadrupeds the extremities 

 of the toes are arranged in a semi-circle, when they are all applied to the ground. 

 In the act of running the heel and wrist are raised, throwing the weight of the 

 body upon the median digits. An infinite repetition of this posture in digitigrade 

 creatures unable to withstand the attacks of their enemies and whose only escape 

 was in flight, the strengthening of the median digits, and the consequent reduc- 

 tion of the outer ones, would follow according to the law of use and disuse of 

 parts. This subtraction of toes has progressed step by step, until the modern one- 

 toed horse has been reached. 



In conclusion I may say that by resort to natural methods for explanation 

 of these modifications we at once bring the subject within the compass of rational 

 understanding, but, if on the other hand we invoke supernatural influence, we im- 

 mediately step into a realm about which the science of palaeontology knows abso- 

 lutely nothing and one which is diametrically opposed to the spirit of modern 

 scientific research. 



The EngUsh have admitted the success of the electric light. Lamp posts 

 have been erected in Bristol. The Lancashire and Yorkshire Railway Company 

 illuminate their station platforms with it and regard it cheaper than gas. Aln- 

 wick Castle, the seat of the Duke of Northumberland, has also been illuminated. 

 The library, a very large apartment, is lighted by three lamps, and the eflfect is 

 reported superior to any light before used. 



* "On the Origin of Foot Structures in the Ungulates," American Naturalist, April, 1881. 



