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 
I'1G. 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 ; 
