52 



HORSESHOEING. 



Fig. 35. 



Cross-section of the wall, mag- 

 nified : a, horn-tubes ; 6, intertu- 

 bular horn. 



li). In front of the median lacuna the two branches unite to form 



the body of the frog (Fig. 27, /i), which ends in a point, designated 



the -point, apex, or summit of the frog. 

 On the upper surface of the frog, di- 

 rectly over the median cleft of the 

 lower surface, there is a small projec- 

 tion called i\v% jrog-&tay (Figs. 29, I, 32, 

 and 33, 6), which fits into the median 

 cleft of the plantar cushion. Besides, 

 the upper surface of the frog shows 

 many minute openings, similar to but 

 smaller than those of the sole and 

 coronary groove, for the reception of 

 villi. In unshod hoofs the frog, sole, 

 bars, and bearing-edge of the wall are 



on a level ; that is, the plantar surface of such hoofs is perfectly 



flat. 



The minute structure of the horn can scarcely be considered in detail in an 

 elementary treatise such as this is. However, a few of the most important 

 facts are as follows : 



If we carefully examine a transverse section of the horn of the wall 

 (Fig. 35), sole, or frog, we will see with the naked eye, though much better 

 with a magnifying glass, many minute points quite close to one another, and 

 greatly resembling the small openings which we have seen in the coronary 

 groove of the wall and on the upper surface of the horny sole and frog. If, 

 now, we examine a longitudinal section of the wall (Fig. 34) or sole, we will 

 see a number of fine, dark stripes, which are straight, parallel, quite close 

 to one another, of different widths, and ^vhich are separated by bands of 

 lighter horn also of different widths. A thin section or slice of the wall 

 taken at right angles to the direction of these dark lines (Fig. 35) shows us 

 that the minute points that are visible to the naked eye, when held up to the 

 light or moderately magnified, prove to be small openings (Fig. 35, a). Since 

 these openings, shown in Fig. 35, represent the dark lines shown in Fig. 34, 

 because an opening is found wherever there is a dark line, we must regard all 

 dark lines seen in longitudinal sections of wall, sole, and frog as hollow cylinders 

 or tubes, though they are not always hollow, but are often filled with loosely 

 adjusted, crumbling, broken-down horn-cells. The dark edges of the open- 

 ings (a) consist of thick layers of horn-cells (tube-walls). The entire struo- 



