86 



SCIENCE FROM AN EASY CHAIR 



like one-half of an egg cut through longwise (see Fig. 1 1 

 pf\ These pre-orbital cavities are known in deer, sheep, 

 and antelopes ; they lodge a gland resembling the tear- 

 gland, which has, itself, a separate existence. Similar 

 "glands" are found in the feet and ankle-joints of sheep and 

 deer. The fluid which they secrete probably has an odour 

 (not readily noticed by man) which helps to keep the herd 

 together, or, on certain tracks when the fluid is smeared 



pf 



PREVALSKY'S HORSE DEER 



FIG. it. Skulls of horses and of deer to show the pre-orbital pit or cups pf, 

 and its absence in the Mongolian (Prevalsky's) horse. 



on to herbage. It is a remarkable fact that the skulls 

 of the wild Mongolian horse and of the fossil horse of 

 the cave-men, as also those of the commoner European 

 breeds, have no trace of this pre-orbital cup or of the 

 gland which Hipparion, their three-toed ancestor, pos- 

 sessed. Nor, indeed, have the asses and zebras. But 

 the Southern horse, the Arab, and all the breeds into 

 which his blood has prominently entered as, for instance, 

 the English racer (so-called "thoroughbred") and the 



