8 
THE PHYSIOLOGY OE THE FOOT. 
The human nail, according to Sharpey, is produced from a 
groove in the dermis, hut receives, as it moves forward over 
the laminse, an additional layer of horny matter secreted 
by them ; thus the body of the nail, as Virchow says, “ can 
easily move forwards, pushing itself over a movable substra- 
tum.” The wall of the horse’s foot is, save in the variety of 
horn, perfectly analogous with the human nail, and I see no 
reason why it should be physiologically different. It is easy 
by this view to understand the passage downwards of the 
wall, but if the horny laminse grow from above, how do they 
obtain their firm attachment ? I really cannot understand 
how a hard substance like the laminse, if continually moving, 
could obtain the firm adhesion we know it to possess with 
the soft sensitive laminse. 
But, to leave all analogy, let me ask why the laminse are 
constructed in every way like a secreting structure if not for 
secretion? Of what benefit to mechanical adhesion can be 
their copious blood-supply? 
Doubtless the sensitive laminse supply nutriment to their 
own secretion, but, if the horny laminse be formed by the 
coronary band, it is by no means evident that any further 
nutrition is required. 
My last reason for believing that the sensitive secrete the 
horny laminse I venture to think invincible. 
As the result of injury we frequently find on the inside of 
the wall a horn tumour. I have examined sections of such, 
and found them to be merely an hypertrophied condition of 
the laminse, formed like them of horn, containing no horn 
fibres. That these tumours are formed by the laminse is 
beyond dispute, and that this formation is abnormal in 
quality as in quantity I challenge proof. 
Again, in cases of removal of portions of wall throughout 
their whole perpendicular extent, we find a secretion from 
the laminse resembling in every particular the horny laminse. 
Mr. Greaves calls this “ horny excresence he has known it 
so firm and thick as to safely retain a nail, yet says that in 
such cases there is “ always an absence of horny laminse.” 
Surely this is a mistake, for if we have an adherent horny 
layer, it must present an exact mould of the surface from 
which it is formed, that is, it must have a laminated arrange- 
ment on its attached surface. My examinations of this horny 
deposit lead me to class it with the interfibrous horn found 
in the wall, sole and frog, and constituting entirely the horny 
laminse. Upon this point hangs the whole question, as if 
under any circumstances a given structure secretes a definite 
