434 DISEASES OF THE HOESE'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 

 i , 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 fore-limbs 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. 



