zSo ESSAYS AND OBSERVATIONS 



we leave the fubjedl, to inquire in what 

 parts of the body the different kinds have 

 been obferved. 



From the hiftories we have of aneu- 

 rifms, it is not eafy to determine exaclly 

 what were true ones ; for, although hun- 

 dreds of authors mention them, yet the 

 accurate hiftories of them are bat few. 

 Moft authors, till of late, only tell us, that 

 they found a cyft filled with blood, which 

 had a pulfation during the patient's life j 

 fometimes adding, that the cyft was a di- 

 latation of the aorta, or fome other vefTel : 

 And moft of the later writers content 

 themfelves with defcribing the external 

 appearance of the aneurifmal fac, without 

 having dlfTeded its coats, to determine 

 exadly in what ftate they were. But fince, 

 from the account of an aneurifm of the 

 aorta given by Haller, and from the hi- 

 ftory of the difTedion of four of the aneu- 

 rifmal facs in the cafe of J. Parker, we 

 are fully fatisfied of the exiftence of true 

 aneurifms (in the ftridleft meaning of the 

 words), I may take the liberty of clafTmg 

 iinder this head all thole aneurifms where 



the 



