PHYSICAL AND LITERARY. 239 



perience has fliewn, that aneurifms may 

 be formed in both thefe ways. 



That all the coats of arteries are 

 fometimes dilated, is plain to ocular de- 

 monftration, from the diflecflion of the 

 ancurifmal facs in the cafe of John 

 Parker *. For, in the three fmaller 

 ones of the right fide, the circular fibres, 

 and all the other coats, were traced di- 

 ftindlly over the whole circumference of 

 the tumours : In the one in the left hani 

 they were feen on the fore fide ; and, al- 

 though they could not be traced on the 

 back part, nor be at all obferved in 



the 



• Jt may feem furprifing that 1 ihould quote (6 parti* 

 cularly this cafe for a faft now fo generally looked upon 

 as common. The reafon of it is, that, although we have 

 many hiftorics of cafes of true ajaeurifms related, yet I 

 have not found one of all thofe 1 have examined, where 

 the different coats of the arteries have been traced by dif- 

 fedion, continued over the whole circumference of the 

 aneurifmal facs, Haller is the only good anatomift who 

 fays he obferved ail the arterious coats, particularly the 

 mufcular, in an aneurifra. But then he gives no figures 

 cf thefe coats; nor is he particular in the hiftory of their 

 d'fledion, £ee his account of an aneurifra of the aorta, 

 Opufcul. Pathologic. Obferv. i8. 



