58 HORSESHOEING. 



frog (Fig. 31, I) divides it into two branches (Fig. 31, i), 



which, pass backward and outward into the hornj bulbs (Fig. 



31, k). In front of the median lacuna the two branches 

 unite to form the body of the frog 

 Fig. 41. ^ (j^ig^ 31^ J^^^ ^l^i^h ends in a point, 



designated the point, apex, or summit 

 of the frog. On the upper surface of 

 the frog, directly over the median cleft 

 of the lower surface, there is a small 

 projection called the frog-stay (Figs. 35, 

 Z, 38 and 39, h), which fits into the 

 median cleft of the plantar cushion. 

 Besides, the upper surface of the frog 

 Cross-section of the wall, mag- shows many miuutc opcuijigs, similar 



f^h't/h ''°'°-*"^^'= ^' ''^*^'- to but smaller than those of the sole 



tubular horn. 



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 de- 

 tail 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. 41), 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 sec- 

 tion of the wall (Fig. 40) or sole, we will see a number of fine, dark 

 stripes which are straight, parallel, quite close to one another, of dif- 

 ferent widths, and which 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. 41) 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 opening's (Fig. 41, a). 

 Since these openings, shown in Fig. 41, represent the dark lines shown 

 in Fig. 40, because an opening is found wherever there is a dark line, 

 we must regard all dark lines seen in longitudinal sections of wall, 



