Hons'-^s HOEING. 585 



yield readily to moderate liniriT pressure, l)Ut from various causes 

 may underj^o ossifieatidn, in which condition they arc hard and un- 

 yielding:. The plantar cushion is n \ved<2:e-shaped mass of toujxh, 

 elastic, fibro-fatty ti.ssue fillinj; all the space between the lateral car- 

 tilaires, forminir the fleshy heels and the tle>^hy fi-ojr. and servincj as a 

 builVr to dispcr.se shock when the f(~ot is .set to the jjiound. It ex- 

 tends forward underneath the navicidar l)one and perforans tendon, 

 and protects these structures from injurious pressure fr(^m below. 

 Instantaneous photoirraphs sliow that at speed tlie horse sets the 

 heels to the jjround beftn-e other parts of the foot — conclusive proof 

 that the function of this toujrh. elastic structure is to dissipate and 

 render harndess violi-nt impact of the foot with the ^jround. 



The horn-producinjr membrane, or " quick," as it is commonly 

 termed, is merel}' a downward ]>rolonf!;ation of the "derm," or true 

 skin, and may bo conveniently called the pododerm (foot skin). The 

 pododerm closely invests the coffin bono, lateral cartilages, and 

 plantar cushion, much as a sock covers the human foot, and is itself 

 covered by the horny cajisule, or hoof. It differs from the external 

 skin, or hair skin, in having no sweat or oil glands, but, like it, is 

 richly sui)i)lied with blood vessels and sensitive nerves. And, just 

 as the derm of the hair skin proiluces upon its outer surface layer 

 upon layer of horny cells (epiderm). which protect the sensitive and 

 vascular derm, .so, likewise, in the foot the i)od<Klorm produces (jver 

 its entire surface soft cells, which, pushed a\\ay by more recent cells 

 tonning beneath, lose moisture by evaporation and are rapidly trans- 

 formed into the corneous material which wo call the hoof. It is 

 proper to regard the hoof as a greatly thickened opidorm having 

 many of the qualities possessed by such epidermal structures as hair, 

 fcathei-s, nails, claws, etc. 



The functions of the pododei-m are to jn'odnce tlio hoof niid to unite 

 it firmly to the foot. 



There are five ])art.s of the pododern, easily distinguishable when 

 the ho( f has been removed, namely: (1) '1 he ]iorioplic i)and, a nar- 

 row ridge from one-sixteenth to one-eighth of an inch wide, running 

 along the edge of the hair from one heel aiound the too to the other. 

 This band i)roduces the perioplic horn, the thin varnishlike layer of 

 glistening horn, which forms the surface of the wall or ''crust," and 

 whose purpose seems U> be to retard evaporation of moisture from 

 the wall. (2) The coronary band, a prominent lloshy cornice encir- 

 cling the foot just below and parallel to the perioplic band. At the 

 heels it is reflected forward along the sides of the fleshy fi'og. to bo- 

 come lost near the apex of this latt«M- structure. The coronet i)ro- 

 duces the mid<lle layer of tin- wall, and the reflexed portions produce 

 the "bars," which are. therefore, to Ih> regarded merely as a turning 

 forward of the wall. (.3^ The fleshy leaves. rtOQ to <500 in number, 



