238 



TEETH OF HORSE 



CHAP. 



the premolars, with the exception of the first, resemble the molars 

 in their pattern. The orbit is completely surrounded by bone. 

 The incisors are chisel-shaped, with a pit on the free surface. 

 The canines are rudimentary if present. The radius and ulna 

 are fused, as are the tibia and fibula. Although for the sake of 

 uniformity a family, Equidae, is here separated from its allies, it 

 is quite impossible owing to the full state of our knowledge of 

 this group to draw a really hard-and-fast line between this family 



FIG. 124. Side view of skull of Horse with the bone removed so as to expose the whole 

 of the teeth, c, Canine ; Fr, frontal ; i 1 , i 2 , &, incisors ; Z, lachrymal ; m\ m 2 , m 3 , 

 molars ; Ala, malar or jugal ; MX, maxilla ; No, nasal ; oc, occipital condyle ; Pa, 

 parietal ; pm l , situation of the vestigial first premolar, which has been lost in the 

 lower, but is present in the upper jaw ; pm?, prr<?, pm*, remaining premolars ; PMx, 

 premaxilla ; pp, paroccipital process ; Sq, squamosal. (After Flower and Lydekker.) 



and the Palaeotheriidae. We shall deal presently with the con- 

 jectured pedigree of the Horse, which naturally involves that 

 family, and which presents an unbroken series from four -toed 

 Perissodactyles to the present one-toed Horse, the various bones 

 and teeth becoming modified in the course of the descent " with 

 the regularity of clockwork." We are compelled to draw the 

 line at functional second and third toes ; directly these are no 

 longer used the animal is a Horse in the strict sense ! This is 

 irrational and regrettable, but necessary for practical purposes, if 



