PATHOGENESIS 53 



because the cavity, pointing upward, does not 

 drain and the pus-soaked dead elements of the 

 hgament remaining stubbornly attached to the 

 living, favor the gradual onward march of the 

 process of destruction. Those originating pos- 

 teriorly travel forward into the ligamentum 

 nuch^ under the connective tissue of the mane 

 and thus seat themselves at just the same point 

 as the atypical form, the chief difference being 

 the amount of bone involvement, which in the 

 atypical form is always more pronounced than 

 in the other. Beginning at the highest point 

 of the withers from a serious pressure necrosis 

 from the harness, this form is more prone to 

 travel downward into the spines, ofttimes at- 

 tacking two or more of them with an acute 

 destructive osteitis that travels down toward 

 the bodies of the vertebrae casting off se- 

 questra and fusing them together with a mass 

 of connective tissue that is very slow to recon- 

 nect itself to the surrounding integuments, 

 even after the pathological process has other- 

 wise terminated. 



Tlie disease is most common in horses whose 

 withers are thin of flesh from hard work and 

 privation. The vitality thus reduced is a dom- 

 inating etiological factor. The enfeebled tissue 

 becomes the prey of tlie virulent infection in- 

 troduced through and harbored by the harness 



