

1895.] on the Structure and Function of the Horse's Foot. 555 



possessing neither blood-vessels nor nerves; the first is called the 

 sensitive, the other the insensitive foot, and the two fit together much as 

 a finger fits into a glove.* 



Various names have been given to the different parts of the foot : 

 for instance, the wall is the portion visible when the foot is on the 

 ground ; the position of the sole is obvious ; whilst a wedge-shaped 

 piece of horn placed in the central and posterior part of the foot is 

 vulgarly known as the " frog " — we shall speak of it as the foot-pad ; 

 finally, a portion of the wall inflected at the heels forms a part known 

 as the bars. 



It is impossible to completely grasp the function and structure of 

 the foot unless we possess some information as to the nature of horn. 



If horn be examined under the microscope it is found to consist of 

 cells which resemble the scales found on the skin ; in fact, hoof is 

 modified skin, the cells forming which have, by a process of com- 

 pression and chemical change, become converted from scales of skin 

 to scales of horn. 



The essential microscopical feature is the presence of canals, 

 around and between which the cells are arranged, uniting and 

 knitting the parts together in such a way as to produce the tough 

 yielding material known as horn. The tubes run through the entire 

 length of the structure ; they are not completely hollow, as the name 

 might imply, but are lightly packed with very soft cells. 



Horn which is dry, as in any of the feet on this table, is as brittle 

 as glass, and fractures like a piece of glue. Horn which is moist cannot 

 be broken ; it can be twisted and torn, but only with difficulty. Under 

 pressure the moist horn yields, the dry horn breaks. 



The moisture in the foot is something very remarkable : in the foot- 

 pad it amounts to 42 per cent., whilst in the wall, which is the driest, 

 it falls to 24 per cent. The use of this moisture is to keep the foot 

 pliable and yielding ; where, therefore, the greatest yielding is required 

 there the moisture is the largest, and where resistance is most needed 

 there the moisture is the least. I shall constantly have to refer to 

 the moisture in horn, for, as you will see later, it is the essential factor 

 in the foot around which all the others work. 



It is through the cells and tubes in the horn that a constant 

 passage of water occurs, by which means the foot maintains, in spite 

 of the evaporation which is taking place from it, the amount of 

 moisture it requires. 



We spoke of the sensitive being buried within the insensitive foot ; 

 it is from this sensitive foot that the horn is secreted, the process 

 being a slow and gradual one. If we examine a horn-secreting surface, 

 it will be found covered with delicate projections known as papillas, 

 about one-quarter to one-half inch in length ; these papillae fit into 



* A working model of the font, twelve times its natural size, was kindly 

 built for this lecture by Captain Gillespie, Army Service Corps, to whom I am 

 very greatly indebted. 



