206 DISEASES OF THE FEET. 



altered wall breaks off at its lower part, and splits both horizontally 

 and vertically. 



The accompanying lameness, which always increases with work, 

 is marked by a shuffling sty*le of progression, especially when both 

 fore feet are affected. The lameness may, after a rest, disappear 

 for the time being; but only to return on the resumption of work. 



The CAUSE of this disease appears to be unknown. 



The TREATMENT is similar to that of "seedy-toe." The 

 affected horn at the coronet should be kept closely pared down. 

 Paraffin oil is a good dressing. 



Navicular Disease. 



NATURE AND PROGRESS.— This disease (Figs. 67, 68 and 69) probably 

 begins as inflammation of the navicular bone, or of the cartilage upon its 

 lower surface. The chronic inflammation set up in the bone produces 

 changes in the substance of the bone, somewhat similar to those of 

 osteoporosis ; in fact, we have " rarefying ostitis," in which the affected 

 portion of compact bone is " slightly redder than natural ; the openings of 

 the Haversian canals after a time become somewhat increased in size, and 

 consequently a larger number are visible to the naked eye. As the process 

 advances, the Haversian canals increase at the expense of the bone surround- 

 ing them, and when they reach a sufficient size they can be seen to contain 

 a small quantity of pink granulation tissue surrounding the vessel. If a 

 portion of the bone at this stage be macerated, it presents a porous, spongy 

 appearance." (Erichsen). Here we have a case of what we may call caries. 

 If pus be present, we shall have ulceration of bone. Owing to the presence 

 of inflammation in the substance of the bone or in the cartilage, small nodules, 

 with or without ulceration, form on the lower surface of the navicular bone, 

 over which the perforans tendon plays, and there is destruction of the 

 cartilage of the joint. Apparently owing to the roughness of the once 

 smooth gliding surface, inflammation is set up in the opposing portion of 

 the perforans tendon, and in the synovial bursa, which lies between the 

 tendon and the affected surface of bone, so that the tendon, in old cases, 

 becomes more or less worn through. In the further progress of the disease, 

 the weakened navicular bone may become fractured by the pressure of the 

 tendon on its lower surface ; the tendon may fray out to such an extent 

 that it will break in two ; it may become adherent to the navicular bone ; or 

 the abraded portion of tendon may continue to work over its rough pulley 

 with great discomfort to the animal, which in any case will suffer more or less 

 pain from movement. N-aturally, a long rest will favour union between the 

 diseased bone and the abraded tendon. 



The (lower) surface over which the perforans tendon plays, is the only 

 surface of the navicular bone which becomes affected in this disease. The 

 other two surfaces, which form a joint with the pedal bone and short pastern 

 bone (Figs. 61 and 70) always remain free from morbid change brought on 

 by this malady. 



On referring to Fig. 70, we see that the perforans tendon is attached to 

 the base of the pedal bone, and passes behind the navicular bone, which 

 forms a pulley for it. On leaving the navicular bone, this tendon passes 

 behind the pastern, fetlock joint, suspensory ligament, and knee, and is, 

 finally, united to the muscle, by the contraction of which the foot is flexed. 

 A horse affected with navicular disease is said, in stable parlance, to be 

 " groggy." 



