238 ESSAYS AND OBSERVATIONS 



tumour ; and thofe mixed^ where an ar- 

 tery has been firft dilated, but afterwards, 

 by the great ftretching or erofion of its 

 coats, they have given way : and the blood 

 has either diftended the neighbouring 

 cellular membranes into one cyft, or dif- 

 fufed itfelf every where through its 

 cells *. 



PARTI. 



Of True Ancurijms, 



For a long time, it was a 'matter of 

 difpute, whether, in the true aneurifm, all 

 the coats of the arteries were dilated, or 

 whether fome of them, particularly the 

 circular fibrous, commonly called mus- 

 cular, was not always ruptured or wound- 

 ed before the force of the blood was ca- 

 pable of dilating the veffel. Later ex- 

 perience 



• Lancifi thinks that dilatations of the ventricle of 

 the heart fliouid likewile be called aneurlfbas ; but ia this 

 he is not generally followed. 



