612 THE DISEASES OF THE HORSE 



"When a foot is examined after death which is known to have been 

 the subject of navicular disease, the parts implicated are invariably either 

 the navicular bone, or the soft parts in contact with it, or often all together. 

 Most frequentl)^ on dividing the tendon of the flexor perforans and turning 

 it down so as to expose the back of the joint between the navicular and 

 coronal bones, that part will be greatly thickened and inflamed, the tendon 

 being often adherent to it. In the healthy condition there ought to be no 

 adhesion of the fibres of the tendon to any part of the navicular bone but 

 its postero-inferior edge, to which the tendon is fixed by some few fibres, 

 the bulk passing on to be inserted in the os pedis. The posterior face of 

 the navicular bone should be beautifully smooth, and lined by synovial 

 membrane which forms a lubricating sac for it to play upon, and thus take 

 off the friction between the tendon and the bone. Such is Nature's provision 



Fia. 105.— UtCEnATiON or the Posteriob Surface of the Navicular Bone. 



1. Lower or plantar surface of pedal-bone. 2. Small specks of exostosis. 



3. Carious patch. 



against mischief in this delicate part of the machinery of the foot, which 

 she keeps in order by the constant supply of synovia or joint-oil. But 

 when the sac is not stimulated to a healthy action by the pressure of the 

 frog below it indoors and out, synovia is no longer secreted in proper 

 quantity, and as soon as the horse is put to hard work inflammation takes 

 place for want of it. The result is some one of the consequences of inflamed 

 joints. Either ulceration takes place in the postero-inferior sui'face, where 

 the tendon glides over it as shown in Fig. 105 (at 3), sometimes ending in 

 caries of the bone itself ; or adhesion takes place without ulceration of the 

 tendon with the surface of the bone, or there are small exostoses thrown 

 out see Fig. 105 (2), or lastly there is simple inflammation without either 

 adhesion or ulceration, and in this stage the disease is amenable to treat- 

 ment without leaving any trace behind. 



The Symptoms of navicular disease are the same, whether the mischief 

 has extended to ulceration or not ; but the history will guide us in ascer- 

 taining how far it has gone. Of course they vazy in degree, for there may 

 be only a slight extent of ulceration, or a high degree of simple inflammation ; 



