Horny Excrefcences of the Human Body • 1 03 
the hair found in the cyft correfponds in appearance with that 
which grows upon the body of the animal ; and when incyfted tu- 
mors of this kind form in flheep, they contain wool. What is ft ill 
more curious, when fuch cyfts are laid open, the internal fur- 
face undergoes no change from expofure, the cut edges cica- 
trize, and the bottom of the bag remains ever after an external 
furface. Different fpecimens, illuftrative of the above-men- 
tioned circumftances, are preferved in Mr. Hunter’s collec- 
tion of difeafes* 
The cyfts that produce horny excrefcences (which are only 
another modification of cuticle) are very improperly confidered 
as giving rife to horns; for if we examine the mode in which 
this fubftance grows, we fhall find it the fame with the human 
nails, coming diredly out from the furface of the cutis. It 
differs from the nails in not being fet upon the fkin by a thin 
edge, but by a furface of fome breadth, with a hollow in the 
middle, exa&ly in the fame manner as the horn of the rhino- 
ceros* ; at leaft this is evidently the cafe in the fpecimen pre- 
ferved in the Britifh Mufeum, and in one which grew out from 
the tip of a fheep’s ear ; they are alfo folid, or nearly fo, in 
their fubftance. 
This mode of growth is very different from that of horns, 
which are all formed upon a core, either of bone or foft parts, 
by which means they have a cavity in them ; a ftrudure pecu- 
liar to this kind of cuticular fubftance. 
Incyfted tumors in different animals would appear, from 
thefe obfervations, to be confined in their produdion to the 
* The horn of the Rhinoceros is a cuticular appendage to the lkin, fimilar to 
nails and other cuticular excrefcences, being in no refpe£t allied to horns but in 
the external appearance. 
cuticular 
