20 PRACTICAL HORSESHOEING. 



rier drives the nails that attach it. The inner face of its 

 upper edge is hollowed out into a somewhat wide concav- 

 ity, which receives, or rather in which rests, the coronary 

 cushion ; this concavity is chiefly remarkable for being 

 pierced everywhere by countless minute openings which 

 penetrate the substance of the wall to some depth ; each 

 of these perforations receives one of the " villi " or minute 

 tufts of blood-vessels already mentioned as prolonged 

 from the face of the membrane covering the interior of 

 the foot. Below this concavity, which receives a large 

 share of the horse's weight, the wall is of about equal 

 thickness from top to bottom ; on the whole of its inner 

 surface are ranged thin, narrow, vertical horny plates, in 

 number corresponding to the vascular laminae, between 

 which they are so intimately received or dovetailed — a 

 horny leaf between every two vascular ones — that in the 

 living or fresh state it is almost impossible to disunite 

 without tearing: them. The inner face of the lower mar- 

 gin is united in a solid manner to the horny sole through 

 the medium of a narrow band of soft, light-colored horn, 

 situated between the two, and which we may call the 

 " white line " or " zone." 



The outer surface of the wall is generally smooth and 

 shining in the natural healthy state. 



The dimensions of the wall vary in different situations ; 

 in front it is deepest and thickest, but toward the quar- 

 ters and heels it diminishes in height and becomes thin- 

 ner ; at its angles of inflection — the points of the heels — it 

 is strong. Its structure is fibrous ; the fibres pass directly 

 parallel to each other from the coronet to the ground, 

 each fibre being moulded on, as it is secreted by, one of 

 the minute tufts of blood-vessels lodged in the cavity at 

 the coronet. Microscopically, the wall is composed of 

 minute cells, closely compressed, and arranged vertically 

 around each fibre, and horizontally between the fibres. A 



