34 



HORSESHOEING. 



rangular plates, attached to the wings of the os pedis, and ex- 

 tending so far upward and backward that one can feel them 

 yield to pressure on the skin above the coronet, and can thus 

 test their elasticity. The perforans tendon and the plantar 

 cushion lie between the lateral cartilages, and on the sides and 

 behind are partiahy enclosed by them . The internal concave sur- 

 face of the lateral cartilage is attached to the plantar cushion, the 

 OS pedis, and the navicular bone, and, like the external, slightly 

 convex surface, is covered with many blood-vessels (veins). 



The plantar cushion (Figs. 18 and 19) is composed almost 

 entirely of yellow elastic and white fibrous tissues, with adipose 



Fig. 19. 



Fig. 18. 



Plantar cusMon seen from be- 

 low : a, base or bulb of the plantar 

 cushion ; &, summit ; c, median 

 lacima or cleft in which lies the 

 ' ' frog-stay' ' of the homy frog. 



Plantar cushion seen from above : a, base 

 (bulbs) of same ; 6, summit ; c, supensory liga- 

 ment of plantar cushion ; d, place at which the 

 elastic ligament connecting the os suffraginis 

 and the lateral cartilage unites with the plan- 

 tar cushion. 



(fat) cells distributed throughout their substance. It is similar 

 in form to the horny frog, and lies between it and the perfo- 

 rans tendon (Fig. 20, a). The bulbs are formed by the pos- 

 terior thicker portion which lies between the lateral cartilages 

 and is divided into two parts by the cleft or median lacuna (Fig. 

 18, e). The summit is attached to the plantar face of the os 

 pedis in front of the semilunar crest, and the bulbs are attached 

 to the lateral cartilages. It is covered inferiorly by the velvety 

 tissue of the frog (pododerm). 



