VII.] 



THE EXTERNAL SKELETON. 



279 



38. Lastly may be noticed certain exceptional though not 

 unfamiliar structures which come perhaps more conveniently 

 under the head of the exo-skeleton than elsewhere namely, 

 the BONY HORNS OF UNGULATES. In the Oxen, Goats, and 

 their allies, horns exist on the head as bony cores persisting 

 throughout life, and supporting the hollow horns before 

 noticed under the head of " Epidermal Structures." In the 

 Giraffe we meet with three bony prominences which arise as 

 distinct ossifications, and only later anchylose with the skull. 

 These are the pair of short " horns " and the median pro- 

 minence in front of them. They are without doubt exo- 

 skeletal structures. In Deer, however, we meet with bony 

 antlers which are shed annually and are destitute of any 

 horny covering. These may exist in both sexes, as in the 

 Reindeer, but generally in the males only. They arise as 



FIG. 260. SERIES OF ANTI.ERS OF THE COMMON STAG, showing (from No. i to 

 No. 8) the gradual increase (with age) of size and complexity in the antlers 

 developed. 



No. i, the antlers which fall in the second year ; 6, antler of a young "stag of 

 ten ;" 7 and 8, antlers of seven years old and upwards. 



soft, highly vascular prominences, and when full grown 

 become hardened by calcareous deposit In some months 

 the investing skin dries up and is rubbed away, and the horn 

 itself falls off after the breeding season, leaving a stump, 

 whence it shoots again in the following year. 



Antlers, as a rule, are branched more so as the individual 

 is older till maturity be attained. 



