70 THE HORSE. 



afforded by means of this gland, and ultimately led 

 to the elimination of the organ itself. It may be 

 that a change from a life habitually passed in forests 

 or scrub to one in open plains would be sufficient to 

 account for such a modification in structure. In 

 any case, it is one which must be very easily brought 

 about, without any other great changes, as the mod- 

 ern ruminants show, being present or absent in them 

 quite irrespectively of real affinity, as indicated by 

 more fundamental and less superficial and adaptive 

 structural characters. It would be interesting to make 

 a careful microscopical examination of the skin of 

 this region in all existing species of Equidce, to as- 

 certain whether any traces of the gland can be found ; 

 for it is present in a most rudimentary condition, 

 without showing any impression on the surface of the 

 bone below in several of the existing Bovidce, the 

 sheep, for instance. In this animal, its place in the 

 economy of life is supplied by the curious little bot- 

 tle-like glandular pouches placed between the toes. 



Another easily-recognized distinction between 

 the hipparion and all modern horses is seen in the 

 structure of the upper molar teeth. The anterior 

 inner cusp of the primitive form (Fig. 10, a.i.) con- 

 stitutes a distinct column instead of being, as in the 

 horse, united for its whole length with the rest of the 

 tooth. The foldings of the enamel are also devel- 



