CHORD. VI A 



383 



which is later rubbed off; the latter consist of a bony core, over 

 which is a chitinous layer, the external horn. Antlers develop 

 only in the male, except in the reindeer, where they appear in 

 both sexes and are annual structures, developing each season and 

 then dropping off. The horns on the other hand are usually pres- 

 ent in both sexes and as a rule are permanent throughout adult 

 life. The short horns on the head of the giraffe are non-decidu- 

 ous, and resemble the antlers of the deer in that they are true 

 bony structures, but are always covered by the skin. The giraffe 



Fir,. ^74. Ovibos mosckatus, the barren ground musk ox, found only in arctic Ami 

 (From a photograph provided by the American Museum of Natural History.) 



is a native of Africa. Deer are found over the whole habitable 

 world, except in Australia and Africa, and include a large num- 

 ber of species. A few are without antlers, like the musk deer of 

 central Asia, but in the great majority they are well developed. 

 Here belong the various species of true deer, such as the axis 

 deer of India, the red deer of Europe, the wapiti or American 

 elk of Canada and the northwestern United States, and the 

 Virginia deer, the Mexican deer, and the mule deer, --all three 

 found in this country, — as well as several species living in South 

 America, and also the reindeer and moose (Fig. 374), or elk as 



