648 



MAMMALIA. 



common integument of the head. In others, as in the Ox, Goat, 

 Antelope, Sec. the Fig. 302- 



bony nucleus of the 

 horn is covered over 

 with a sheath of cor- 

 neous matter, giving 

 it a hard and smooth 

 surface. 



Both the above 

 kinds of horns are 

 persistent; but in the 

 Deer tribe the de- 

 fences of the head, 

 which are large and 

 branched, are deci- 

 duous, being formed 

 every year from a 

 vascular skin that 

 covers them exter- 

 nally during the pe- 

 riod of their growth, 

 but shrivels up and 

 dries when they are 

 completed. These 

 horns fall off after a 

 certain time, to be 

 renewed again the 



following season ; the mode of their formation will, however, be 

 examined in another place. 



(729.) In consequence of the weight of the horns in such spe- 

 cies as possess weapons of this description, the head is necessarily 

 extremely heavy ; and in genera where the horns are wanting or 

 feebly developed, as in the Camel or the Giraffe, such is the length 

 of the neck, that, even with a disproportionately small head attach- 

 ed to the extremity of so long a lever, incessant and violent mus- 

 cular exertion would be needed to sustain or to raise it from the 

 ground. This difficulty is obviated by a very simple and elegant 

 contrivance : a broad band of ligament, composed of the same 

 elastic tissue as that composing the ligamenta sub/lava of the 

 human spine, is extended from the tips of the elongated spinous 

 processes of the back, and sometimes even as far backwards as the 



