7OO MANUAL OF ZOOLOGY. 



(figs- 355 and 397, D). The functional toe is the 3d, and 

 the 2d and 4th digits are represented only by rudiments of 

 their metapodials ("splint-bones"), hidden beneath the skin. 

 There is a discontinuous series of teeth (fig. 395) in each jaw; 



Fig. 395. Skull of the Horse {Equus caballus). 



and in the males, canines are present, but these are wanting in 

 the females. The dental formula is 



1-3=3. c i^l f QT ?=?V p m 3=3. 3=3 = 40 or 38. 

 33 i i \ o oJ 33 33 



The skin is covered with hair, and the neck is furnished 

 with a mane. 



As regards the dentition of the recent Equidce, there are 



sometimes - - praemolars, but the first praemolar usually dis- 

 4 4 



appears in adult life. The canines are of small size. The 

 outer side of the molars (fig. 396) is deeply grooved, with two 

 parallel sulci, to which internal ridges correspond, their length 

 being very great, and the whole external surface being thickly 

 coated with cement ; while the enamel-ridges and folds of the 

 crown are filled in with the same substance. The enamel cover- 

 ing the incisors is folded in at the crown, like the inverted 

 finger of a glove, the tube thus formed being filled in with soft 

 cement ; and it is the wearing down of this with age which con- 

 stitutes the " mark." 



The family Equidcz is divided by Dr Gray into two sections 

 or genera : JEguus, comprising the Horse and Asinus com- 



