16S jR. S. Lull — The Evolution of the Horse Family. 



description is somewhat highly colored, but a multitoed horse 

 without doubt forms the basis for the legend. 



Changes in the Body. — In the body the evolutionary 

 changes are not so striking, except for an increase in size and 

 length of back. There is also a change of contour, that of the 

 more primitive forms being suggestive of flesh-eating animals 

 rather than horselike. 



Of necessity the neck and head elongate apace with the 

 limbs to enable the creature to reach the ground, although the 

 increase in length of the skull is largely in the facial portion, 

 the cranium being conservative in growth. This is of two- 

 fold benefit, since it not only gives the needful room in the 

 jaws for the rajDidly increasing armament of the teeth, but by 

 raising the eyes above the earth extends the range of vision 

 while grazing. 



Changes in the Teeth. — In the evolution of the teeth we 

 again find both progression and retrogression, as in the mod- 

 ern horse the canine and the first premolar are alike reduced to 

 vestiges and are often entirely absent. The early horses had 

 grinding teeth of a very generalized pattern ; indeed, it is often a 

 matter of great difficulty to distinguish the teeth of these horses 

 from those of the ancestors of what are now widely removed 

 orders of mammals. On their crowns these teeth bore little 

 cusps or prominences, which in the quadrangular molars just 

 begin to grow together into the crests that later form the 

 greater portion of the grinding surface. The premolars are at 

 first simple in character, but as time goes on they become succes- 

 sively molar-like, beginning with the hindermost. This is not 

 true of the anterior one, which, as we have seen, is finally 

 reduced to an often disappearing remnant. 



During the forest-dwelling period in the history of the 

 horses and while they lived upon succulent meadow grasses, 

 the teeth, though increasing in size with the entire organism, 

 remain short crowned. Upon the expansion of the prairies, 

 however, and the adoption of the harsh grasses as a main staple 

 of food, the tooth of the horse changes in character, becoming 

 elongate, prismatic in shape, and the depressions lying between 

 the crests filling with a substance known as cement, which 

 strengthens the entire tooth. The result is a long columnar 

 structure made up of three sorts of material of different 

 degrees of hardness, — enamel, dentine, and cement, which 

 through differential wear always present a roughened grinding 

 surface. 



During the early life of the horse the tooth is continuously 

 growing and, in spite of the fact that it must constantly move 

 outward to compensate for wear, the root penetrates deeper 

 and deeper within the jaw until fully formed. The outward 



