102 GROWTH OP HORNS. 



skin, which wears away ; and after it has remained bare for a 

 certain time, it falls off and gives place to a new horn, which 

 is destined to experience the same changes in its turn. 

 These perishable horns are called antlers; and they are only 

 found amongst animals of the Stag tribe. In other instances, 

 again, the bony axis grows during the whole of life, never falls 

 off, and is covered with a kind of sheath composed of. an elastic 

 substance, named horn, which is analogous to that of the nails, 

 and which increases by successive layers. The name of hollow 

 horns is given to these .appendages, when thus inclosed in a case 



which seems formed of united 

 hairs ; and we find them amongst 

 the different kinds of Oxen, Sheep, 

 Goats, and Antelopes. It is 

 further to be noticed, that in all 

 these animals, with the exception 

 of the Antelope, the bony core 

 of the horns is hollowed out into 

 large cells, which communicate 

 FIG. 55 -HEAD of A GOAT. w jth the frontal sinus of the nose, 



and thus receive air into their interior. 



83. The mode of formation and renewal of the kind of horn 

 known under the name of antler, is very simple, and is worthy 

 of notice in this place. At a certain age, there is developed on 

 each side of the frontal bone, a projection, whose formation may 

 be compared to that of the tumours known in medicine under the 

 name of exostoses, or to that of the callus, which is deposited 

 around the extremities of the ordinary bones in cases of fracture, 

 and which serves to reunite them. These protuberances, whose 

 tissue is very compact, grow rapidly, and raise up the skin which 

 covers them. They receive a great quantity of blood from 

 numerous vessels which run along the surface, and also from 

 those which traverse canals excavated in the interior ; and the 

 formation of new bony substance goes on for a time with great 

 energy. But this very energy soon checks itself; for as new 

 bony matter is deposited in the channels containing blood-vessels, 

 these channels are gradually obstructed, so that the supply of 

 blood is progressively reduced, and at last ceases altogether. *The 



