442 DISEASES OF THE HORSE'S FOOT 



It is, perhaps, even more likely to be confounded with 

 contraction when we have with the contraction a state of 

 atrophy and thrush of the frog. With a frog in this condi- 

 tion pressure will give rise to pain, and navicular disease be 

 erroneously judged to be present. In such a case we must 

 rely wholly upon either extreme flexion or extreme exten- 

 sion of the joint to guide us, when, if contraction only is the 

 offending condition, no symptom of pain will be shown. 



Navicular disease may also be confused with rheumatic 

 affections, with sprain of the posterior ligaments of the first 

 interphalangeal articulation, and with sesamoid lameness. 

 Mistakes are sometimes made, too, especially with a hasty 

 observer, in confounding it with shoulder lameness. 



In rheumatism the constant changing of the seat of pain, 

 the sometimes elevated temperature, and the appearance of 

 symptoms of heat, tenderness, and swelling in the affected 

 area should guide one to a right conclusion. 



In sprain of the posterior ligaments of the coronet and in 

 sesamoid lameness, nothing but a careful examination and 

 manipulation of the jDarts will ward off error, for in each of 

 these cases there is ' pointing ' and resting of the limb, and 

 considerable disinclination to put weight firmly upon it. 

 If at the same time manipulation gives distinct evidence of 

 pain, all doubt may be set at rest. 



Roughly speaking, sesamoid lameness is a condition of 

 the gliding surface of the sesamoids, and the face of the 

 tendon playing over them, similar to that found in navicular 

 disease. All symptoms of pointing, the constant main- 

 taining of the limb in a state of flexion, and a feeling 

 manner of progression are again all present. It is plain 

 from this that in all cases where an animal with a gait at all 

 suggestive of navicular disease is brought for our examina- 

 tion, the manipulation of the limb should be thorough. 

 The character of the lameness is almost sure to deceive us ; 

 and it is not until we are able to obtain local S3'mptoms 

 pointing to the one or the other of the conditions we have 

 enumerated that a decisive opinion may be given. In 

 sesamoid lameness the local symptoms are those of heat 



