434 DISEASES OF THE HORSE'S FOOT 



The navicular bone is what we may term a complement 

 of the os pedis. It exists, in fact, simply in order that the 

 os coronse may have a sufficiently large articulatory surface 

 to play upon. One wonders at first that Nature did not 

 arrive at this by originally placing a larger bone below. 

 Colonel Smith explains this by suggesting that this would 

 in all probability have meant its fracture. In progression 

 the. hind part of the foot comes to the ground first, and 

 upon the hinder portion of the articulation would fall the, 

 first effects of concussion, together with the greater part of 

 the body-weight. A yielding joint was in this position 

 necessary, and that formed by the navicular bone fills all 

 requirements. 



In this connection one next considers the part played by 

 the front limbs during progression. As Zundel expresses 

 it, they are columns of support rather than of impulsion, 

 and, as the body-weight is thrown forward by the hind- 

 limbs, it is the duty of the forelimbs to receive it. The 

 shock or concussion of the body-weight thus thrown for- 

 wards is first received by the muscles uniting the limb to 

 the trunk, and a great part of it there minimized by their 

 sling-like attachment. It is further absorbed by the 

 shoulder- joint, and from there passed on to the almost 

 vertical bony column represented by the radius and ulna, 

 the knee, and the metacarpus. On reaching the first 

 phalanx, a portion of the remaining force is passed on to 

 the front of the phalanges and loses itself in front of the 

 hoof, while the other portion is transmitted to the flexor 

 tendons, finally to the perforans, and to the posterior parts 

 of the foot. During progression, therefore, the navicular 

 bone is constantly pushed downwards and backwards by 

 the bony column, and is just as constantly pushed forwards 

 and upwards by the resistance of the perforans tendon. 

 This means, of course, that the navicular bone is more 

 or less constantly subject to compression, and constant 

 pressure, as we know full well, is a pretty sure factor in 

 bringing about malnutrition of the parts, with atrophy or 

 chronic inflammatory changes as an end result. 



