HORNS OF THE DEEE. 803 



hog, the quills of the Porcupine, the scaly covering of the Manis, and 

 even the armour that defends the back of the Armadillo are all of them 

 but modifications of the same structures, adapted to the altered condi- 

 tions under which the creatures live. Even the horn upon the snout of 

 the Rhinoceros is but an agglomeration of hairy filaments, formed upon 

 a broad and compound pulp. The nails that arm our fingers and toes, 

 the corneous sheath that invests the horns of the Ox and Antelope, 

 nay, the hoofs of herbivorous quadrupeds are all epidermic secretions 

 from the vascular cutis or, in other words, are hairs, altered in their 

 form and extent according to the exigencies of the case. 



(2349.) Widely different, however, are the so-called horns of the 

 Deer tribe, which in reality consist of bone, and, being deciduous, have 

 to be reproduced from year to year by a most peculiar and interesting 

 process. No sooner does the return of genial weather again call forth 

 the dormant reproductive energies of the system, than the budding 

 antlers begin to sprout from the forehead of the Stag, and rapidly ex- 

 pand in their dimensions from day to day. On making a longitudinal 

 section of the young horn, it is found to be continuous with the os 

 frontis, having its outer surface covered with a vascular periosteal 

 membrane derived from the pericranium, which in turn is protected by 

 a fine velvety skin. Moreover, when a growing antler is injected 

 minutely, and its earthy matter removed by means of an acid, vessels 

 derived from the periosteum are found to traverse it in all directions, 

 proving its identity with real bone. As growth goes on, the external 

 carotid arteries, thus called upon rapidly to furnish a prodigious supply 

 of materials, dilate in a remarkable manner, and soon the palm and the 

 antlers of the horn have acquired their full dimensions. No sooner is 

 this accomplished than a prominent ring or burr is formed around the 

 base, which, projecting outwards, compresses and soon obliterates the 

 vessels that have hitherto supplied the growing defences. The circu- 

 lation being thus put a stop to, the soft teguments and periosteum 

 peel off in strips ; and the bone, denuded of its covering, becomes a 

 formidable weapon. 



(2350.) At the close of the breeding-season the removal of the horns 

 is speedily effected: the connexion between their bases and the os 

 frontis is gradually weakened by interstitial absorption, until at length 

 a slight effort is sufficient to detach the branching honours of the Stag, 

 and they fall off, leaving a broad cicatrix : this soon skins over; and the 

 succeeding year calls forth a repetition of the process*. 



(2351.) The CETACEA form a very remarkable group among the hot- 

 blooded Mammifers as relates to the external covering of their bodies. 



* In a physiological point of view this rapid production of osseous matter is truly 

 wonderful. The horns of the Wapiti Deer, thus annually reproduced, will weigh 

 upwards of thirty pounds ; and in the fossil Irish Elk the weight of these deciduous 

 defences must have been greater than that of the entire skeleton. 



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