EEGIONAL ANATOMY 43 



The median ridge widens out as it passes backwards, 

 forming the larger part of the posterior portion of the frog. 

 This median ridge fits into the cleft of the plantar cushion. 

 It serves to prevent displacement of the sensitive from 

 the horny frog, and has been rather aptly termed the 

 ' Frog -stay.' 



The Inferior Surface is an exact reverse of the superior. 

 The triangular depression of the superior surface is repre- 

 sented in the inferior surface by a triangular projection, 

 and the ridge-like frog-stay of the upper surface is 

 represented below by a median cleft, the Median Lacuna 

 of the frog. The triangular projection in front of the 

 median lacuna is the body or cushion of the frog. It is 

 continued backwards as two ridge-like branches, which, at 

 the points of the heels, form acute angles with the bars. 

 On the outer side of each lateral ridge is a fissure. These 

 are known as the Lateral Lacunae. 



The Sides of the frog are flat and slightly oblique. They 

 are closely united to the bars and to the triangular inden- 

 tation in the posterior border of the sole. 



The Base of the frog is formed by the extremities of its 

 branches, which, becoming wider and more convex as they 

 pass backwards, form two rounded, flexible, and elastic 

 masses separated from each other by the median lacuna. 

 These constitute the * glomes ' of the frog. They are 

 continuous with the periople. 



The Point of the Frog is situated, wedge-like, within the 

 triangular notch in the posterior border of the sole. 



4. The Periople, or Coronary Frog Band. — This is a 

 continuation of the substance of the frog around the 

 extreme upper surface of the hoof. It is widest at the 

 heels over the bulbs or glomes of the frog, and gradually 

 narrows as it reaches the front of the hoof. It is, in reality, 

 a thin pellicle of semi-transparent horn secreted by the 

 cells of the perioplic ring. When left untouched by the 

 farrier's rasp it serves the purpose, by acting as a natural 

 varnish, of protecting the horn of the wall from the eft'ects 

 of undue heat or moisture. 



