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 corone 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. Itis 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. 
