10 



AMi:h'/(\\.\ M(s/':rM cijdj-: li-m-lkts 



oil tlic inside 

 surlaccs of the 

 enamel while tlie 

 toolh is siill 

 within tlie jaw- 

 hone; the ce- 

 ment is deposi- 

 ted on the out- 

 side surfaces of 

 tlie enamel after 

 the tooth has 

 broken through 

 the jawbone and 

 )efore it api)ears 

 above the jiunis. 

 \'ari()us othe 

 pecuharities dis- 

 tinguish the 

 horse from most 

 other animals; 

 some of these 



are sliaicd by other hoofed 

 animals. The two lonjz; bones 

 of the forearm (radius and 

 ulna) are sej)arate in the 

 ^I'eatei' number of animals, 

 but in the hoise and in man}' 

 othei' hoofed animals, they are 

 consolidated into a single bone 

 (See Fig. 17, j). 27). The same 

 consolidation is seen in the 

 bones of the lower leg (tibia 

 and fi})ula). (Hee 

 Fig. 18, p. 28.) 

 The lengthening 

 of the foot and 

 stepping on the 

 end of the toe 

 raises the heel in 

 the horse, as in 

 nian\' other ani- 

 mals, to a con- 



FIG. 2. EVOLUTION OF THE FORE FOOT. PRINCIPAL STAGES 



(Right to Left) 



1. Four-toed horso Eohippus. Kocene Epoch 



2. lOarly three-toed horse Mesuhippus. OhKocene Epoeh 

 ■i Later three-toed horse Merycfiippus. Miocene Epoch 

 4. One-toed horse Equiis. Pleistocene Epoch and Modern 



All outside views showing; the middle and outer digits of the fore foot . In Eohip- 

 piis the two outer toes (digits l\ and V) are eoniplete. In ^fel^iohippus, digit V is 

 reduced to a .small splint and digit IV is notably smaller than the middle digit. In 

 Mcrifchippus, digit \' is a tiny nodule of hone and digit I\' has l)eeome very slender in 

 comparison with the middle digit. In Equus digit \\ is reducc^d to a long splint, 

 while of the fifth digit no trace remains 



