30 PRACTICAL HORSESHOEING. 



ground on which the animal stands or moves, is unceas- 

 ingly regenerated by the living tissues within. We have 

 already referred to the special apparatus which is more 

 immediately concerned in this work of regeneration, and 

 pointed out that the wall with the laminse on its inner 

 face * is formed from the coronary cushion at the upper 

 part of the foot ; the sole from the living membrane cov- 

 ering the lower face of the pedal bone ; and the frog from 

 the plantar cushion. It has been also mentioned that this 

 dead horny envelop, instead of being merely in juxta- 

 position with this exquisitely sensitive secretory mem- 

 brane, is everywhere penetrated to a certain depth on its 

 inner face (with the exception of the portion of the wall 

 covered with the horny leaves) by multitudes of minute 

 processes named villi, which are not only concerned in 

 the growth of the horn-fibres, acting as moulds for them, 

 and endowing the hoof with that degree of lightness, 

 elasticity, and toughness, which are so necessary to its 

 efficiency, but also make this insensitive case a most use- 

 ful organ of touch. 



The growth of the horn takes place by the deposition 

 of new material from the secreting surface ; this deposi- 

 tion is effected at the commencement or root of the fibres ; 

 where the horn is yet soft, and its incessant operation 

 causes these fibres to be mechanically extended or pushed 

 downward toward the ground in a mass. Once formed 

 they are submitted to no other change than that of be- 

 coming denser, harder, less elastic, and drier, as they 

 recede farther from the surface from which they origi- 

 nated. 



So regular is this growth, generally, in every part of 



* It is generally stated that the horny leaves are formed by the sensi- 

 tive ones, with which they are in such close union. That this is an error, 

 the microscope, physiology, and pathological experience, abundantly tes- 

 tify. 



