104 Mr. Homers Obfervatlons 'bn 
cuticular fubftance proper to the animal in which they take 
place; for, although cuticle, hair, nail, hoof, and horn, are 
equally productions of animal fubftance, only differing in tri- 
vial circumftances from each other, we do not find in the 
human fubjeCt any inftance of an incyfted tumor containing a 
fubftance different from the cuticle, hair, and nails of the 
human body, to which laft the horny excrefcences, the fub- 
je<t of the prefent Paper, are certainly very clofely allied, both 
in growth, ftruCture, and external appearance ; and when of 
fome length, they are found to be fo brittle as to break in two, 
upon being roughly handled, which could not happen either to 
hoof or horn. In thefheep they produce wool inftead of hair; 
and in one inftance in that animal, where they gave rife to an 
horny excrefcence, it was lefs compact in its texture, and lefs 
brittle than fimilar appearances in the human fubjeCt ; upon 
being divided longitudinally, the cut furface had more the ap- 
pearance of hoof, and was more varied in its colour than nail. 
Incyfted tumors being capable of producing horns, upon 
the principle we have laid down, is contrary to the ufual 
operations of nature; for horns are not a production from 
the cutis, and although not always formed upon a bony 
core, but frequently upon a foft pulp, that fubftance differs 
from common cutis in its appearance, and extends a confidera- 
way into the horn : it is probable, that this pulp requires a 
particular procefs for its formation *. 
^ A fheep, -about four years old, had a large horn, three feet long, growing 
upon its fiaiik. It had no connection with bone, and appeared to be only attached 
to the external Ikin. It dropped off in confequence of its weight having produced 
ulcetation in the foft parts to w r hich it adhered. Upon examining it there was 
a flefhy fubftance, feven inches long, of a fibrous texture filling up its cavity 
upon which the horn had been formed. 
3 
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