INTRODUCTION. 9 



warts become transformed into a tissue identical with 

 horn. Such a specimen is represented in fig. 4. It 

 shows a large horn projecting from the forehead of 

 a cow, the horn is fifty centimetres in length. It 

 was obtained by the celebrated John Hunter, and 

 is preserved in the museum of the Royal College of 

 Surgeons. A careful examination of the horn and the 



FIG. 5. The head of the Rhinoceros, showing the nasal horns, 

 physiological type of wart-horn. 



material which occupied the cavity in the horn, indicate 

 that it originated in a wart. Such horns are common 

 in man, and have been known to attain a large size. 

 A physiological type of such horns is furnished by the 

 nasal horn of the rhinoceros which in its structure, con- 

 nections, and mode of origin resembles in its main par- 

 ticulars the pathological horn on the head of the cow ; 



