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The base of the posterior extremities constitutes the heels or 

 bulbs of the frog. These are two round, flexible, and elastic 

 eminences formed by the two extremities and separated by the 

 cleft. These extend upward and are continued around the exter- 

 nal part of the superior surface of the wall in the form of a band, 

 which is the coronary frog band. It is from this, on its inferior 

 border, that the thin covering of the hoof is continued. 



It is an acknowledged fact that white hoofs, like white skin, 

 are more delicate, porous, and prone to disease than dark ones. 



The parts contained within the hoof are the os pedis, os navic- 

 ularis, and the lower extremity of the os coronce, the ligaments 

 by which they are connected together, insertions of the extensor 

 pedis, a,-aA. flexor perforans tendons, the blood vessels, and nerves. 



There are also certain other structures proper to the foot, viz, 

 lateral cartilages, sensitive frog, coronary ligament, sensitive 

 laminoe, and sensitive sole. 



The lateral cartilages are of an irregular, quadrangular form, 

 situated inside the quarter and attached to the wings of the cof- 

 fin bone. Attached to the inner surface of the hoof is the sensi- 

 tive portion of the hoof, which may, like the hoof itself, be divided 

 into the regions of the wall, the sole, the frog, and the coronary 

 band. The keratogenous membrane is a sensitive sheath which 

 envelops the os pedis. Its outer surface is endowed with the 

 function of secreting horn tissue for the renewal of the various 

 parts of the hoof. 



Tlie sensitive frog or plantar cushion. 



The sensitive frog occupies the posterior and central parts of 

 the foot, filling up the irregular space between the lateral carti- 

 lages, flexor tendon, and os pedis, bounded laterally by the lateral 

 cartilages, above by the flexor tendon and below by the homy 

 frog. It is continuous with the sensitive bars, sole, and the coro- 

 nary ligament. The base looks backward and is divided into 

 bulbous enlargements, which are united to the lateral cartilages. 

 The external layers secrete the horny frog. 



Coronary substance or coronary bend. 



This is the vascular substance which occupies the coronary 

 groove on the superior border of the wall. It consists of a dense, 

 fibrous mass or band, which is connected with the coffin bone and 



