PATHOGENESIS 39 



character, it gradually enlarges into a cyst of 

 larger and larger dimensions until it becomes 

 clinical by bulging at the surface of the base 

 of the neck or at a point of least resistance 

 adjacent thereto. The sac is at first very small 

 and without any well developed limiting mem- 

 brane but as it becomes larger the tissues react 

 to the encroachment by forming a firm con- 

 nective tissue layer around it and at the same 

 time fibrin and cells attach themselves to the 

 inner wall and thus pave it with a smooth 

 carpet that completes a firm encapsulation of 

 the liquid contents. The amount of connective 

 tissue contained in the encapsulating structure 

 varies with the chronicity of the process. In 

 old, slotdy forming cases the fibrous elements 

 may form in large quantities, encroaching upon 

 the capacity of the sac internally and gradually 

 bulging exteriorly until the lesion is in fact 

 more fibrous than cystic. Thus ice have the 

 large fistulae of the icithcrs in tchich fibrosis is 

 the dominating feature. This sac is uniformly 

 related to one of the dorsal spines, usually the 

 second, but sometimes the third and in rare 

 cases the fourth or even the fifth. We have 

 never seen a typical fistula of the withers orig- 

 inate farther back. Those located on the sum- 

 mit or further back are always of the other 

 variety (traumatic or atypical). The point of 



