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THE BONES OF THE TOOT. 



of the bone are most widely separated at the back (fig. 16, d). 

 Each wing is divided by a notch, continuous with the pre- 

 plantar groove, into an upper and lower portion, though in old 

 horses the two parts may be united by exostoses, and instead 

 of a notch a hole alone exists. To the wings are attached the 

 lateral cartilages (fig. 17, B), which we shall afterwards describe 

 more fully. It not unfrequently occurs that these cartilages 

 become ossified, especially at their point of origin, causing the 

 wings of the bone to appear much larger than they really are. 



The three borders of the pedal bone are : an upper, a lower, 

 and a posterior. The upper border runs from one wing to the 

 other, first in a forward and upward, then in a downward and 

 backward, direction, and divides the articular from the anterior 

 surface. It is continued over the pyramidal process, and is 

 somewhat excavated and rough on either side for the insertion 

 of ligaments. 



The lower border divides the anterior from the plantar surface, 

 and is sharp and well-defined. Its centre point often shows a 

 slight notch. As the os pedis is somewhat inclined in the 

 normal position of the hoof, as shown by the section (fig. 10), 

 the anterior part of this border is the low^est portion of bone 

 in the limb. Just above the border are a number of large 

 holes for the passage of arteries. 



The posterior border divides the articular from the plantar 

 surface, and runs obliquely from one wing of the os pedis to the 

 other. Posteriorlv, it is in contact with the navicular bone. 



6. The Naviculak Bone. 

 (Fig. 10, F, and Figs. 19 and 20.) 



This is a short, transversely elongated bone placed between the 

 wings of the pedal bone, articulating with the posterior edge of 

 its upper surface, and assisting to form the cavity for the recep- 

 tion of the lower end of the coronet bone. It possesses an 

 anterior and a posterior surface, an upper and a lower edge, and 

 an inner and an outer extremity. 



The anterior surface is also directed slightly upwards, and is 

 covered with articular cartilage. A vertical ridge divides the 

 surface into two unequal portions, the inner of which is the 

 larger ; both are concave, and with the ridge continue posteriorly 



