MAMMALS 87 



shedding of an antler, but it illustrates the fact that the 

 shedding of dead bone is a normal physiological process. 



Periostitis is very frequent in the legs of horses. In the 

 fore-leg it is generally known as splint ; in the hind-leg as 

 spavin. These affections concern chiefly the carpal and 

 metacarpal bones, or tarsal and metatarsal, as the case may 

 be, and they are usually accompanied by the formation of 

 exostoses. It is stated by Moller that the periostitis, whether 

 in fore-leg or hind-leg, is usually caused by internal strains, 

 not by external injury or irritation. I need not, therefore, 

 discuss these cases, as they are not analogous to the forma- 

 tion of antlers. There are, however, plenty of cases where 

 exostoses are caused on the metacarpal by friction with the 

 hoof of the other leg. Moller states that the two kinds are 

 easy to distinguish clinically, because the exostoses due to 

 external irritation are round, and situated on the large meta- 

 carpal only, while the others are lengthened, and affect the 

 splint bone of the inner side of the leg. 



I am not able to give instances of abnormal exostoses 

 being shed like the antlers of deer, but it is a well-known 

 fact that destruction of the periosteum causes death of the 

 bone it covers, and that dead bone may be extruded. I 

 think, therefore, that if a superficial exostosis were denuded 

 of skin in the horse, for instance absorption at the base 

 would occur, and the exostosis would drop off. 



I have referred above to the effects of castration on the 

 growth of the antlers, and will here state more precisely 

 what has been definitely ascertained concerning these effects. 

 All the evidence of any real value seems to be mentioned in 

 two accounts; a paper by Dr. Fowler, 1 and Caton's work 

 already cited. Some of Caton's experiments were made on 

 mature stags which had large branched antlers. He found 

 that if the testes were removed from the stag after the 



1 I'roc. Zonl. Soc. 1894, p. 485. 



