410 THE HORSE. 



boue presses it against the os corona3, the unprepared state in 

 which this part is allowed to remain is sure to produce inflamma- 

 tion, if the work is carried far enough. Thus in each case the 

 weak part suffers, but occasionally, though very rarely, the foot 

 wnth an arched sole contracts laminitis, and the flat one is attacked 

 by navicular disease; the exceptions, however, are so few that 

 they may be thrown out of the calculation, and from the shape of 

 the foot alone it may almost invariably be pronounced, when a 

 horse is known to be subject to chronic lameness, whether its seat 

 is in the laminre or in the navicular joint. 



When a foot is examined after death which is known t: 

 have been the subject of navicular disease, the parts implicated 

 are invariably either the navicular bone, or the soft parts in con- 

 tact with it, or often all together. Most frequently 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 

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

 which she keeps in order by the constant supply of synovia or 

 joitit oil. But when the sac is not stimulated to a healthy action 

 by the pressure of the frog below it in doors 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 surface, where the 

 tendon glides over it, 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, or 

 lastly there is simple inflammation without either adhesion or 

 ulceration, and in this stage the disease is amenable to treatment 

 without leaving any trace behind. 



The sT/mjyfoms of navicular disease are the same, whether the 

 mischief has extended to ulceration or not; but the history will 

 guide us in ascertaining how far it has gone. Of course they vary 

 in degree, for there may be only a slight extent of ulceration, or a 

 high degree of simple inflammation ; but in the former case the 

 lameness will not be so marked as in the latter, though the prospect 

 of recovery will be much less. There is always more or less lame- 



