526 ANATOMY AND PHYSIOLOGY OF THE HORSe’s FOOT. 
when they have attained a certain length ; and also, in all 
likelihood, because we have not here the laminae which 
appear to confer such solidity and conglutination among the 
fibres of the wall that they grow to an indefinite length, 
carrying the laminae with them. 
The union between the sole and wall is of the most inti- 
mate kind, though they are never blended so thoroughly as 
to be inseparable or indistinct, but may be disunited by 
maceration, disease, and the action of heat. Their junction 
takes place at the margin of the sole by what we have termed 
the “ white line ” — a narrow space of a lighter coloured and 
softer horn than either the wall or sole, and which corre- 
sponds to the interdigitation of the horny and vascular laminae. 
Immediately the border of the sole and the inner face of the 
wall meet, the lateral laminellae we have just described 
cease ; they do not proceed beyond the termination of the 
vascular laminae in the villous prolongations already noticed. 
But we have the horny laminae — now with plane sides and 
retaining their density and firmness — still projecting inwards, 
and instead of the vascular laminae being received within 
them, as above the sole, there are digitations of horn, com- 
posed of fibrous tubes secreted by the tufts of vessels that 
terminate the ends of the podophyllae. It is this horn which 
forms the white line seen by the farrier when paring the 
sole. 
In structure and appearance this white line only differs from 
the sole in the greatly diminished quantity or even total absence 
of pigment, should the hoof be ever so dark coloured ; showing 
that the vascular laminae do not supply colouring matter, 
and affording us additional evidence to that we will hereafter 
adduce, that they do not secrete the horny leaves of the wall. 
The tubes or fibres of the white line are larger and longer 
than those of the sole, and between the keraphyllae are 
usually arranged in a single row — the papillae terminating 
the podophyllae being single ; the cells are loosely aggregated, 
and appear to contain less horny matter than those elsewhere, 
both in the walls of the tubes and the spaces between them ; 
this gives the line a texture and appearance notably different 
from that of the sole and wall, and testifies that the secretory 
faculty of the vascular laminae is not of the same character 
as the parts which furnish these two important divisions of 
the hoof. This white line is easily penetrated by fluids, and 
is much more readily destroyed by maceration than either 
the sole or wall ; in ordinary wear it becomes fissured more 
or less from partial solution of its cells, admitting sand and 
gravel with facility to a certain depth. Its junction or inter- 
