ANEUEYSM OF THE POPLITEAL ABTEBY. 277 



marked evidence of pressure symptoms except upon the sub- 

 jacent lumbar vertebrae and the nerves associated with them. 

 It tends to increase forwards, this being the line of least 

 resistance. 



The popliteal artery has the following anatomical peculiarities 

 which may explain the frequency with which it becomes the site 

 of a sacculated aneurysm. It is constantly being bent in flexion 

 of the knee, whereby a certain amount of strain may be thrown 

 upon it ; it derives little if any support from the surrounding 

 muscles and tendons, and it is close above a bifurcation. 



The position of the vessel upon which an aneurysm forms 

 determines many of the characteristic signs caused by dilatation 

 of the artery and the pressure of the sac upon the surrounding 

 structures. 



The first structure to be pressed upon is its accompanying 

 vein. The popliteal vein is the thickest vein of its size in 

 the body, but is the most adherent to its artery ; hence it 

 follows that pressure upon it soon leads to considerable oedema 

 of the limb on the distal side. The internal and external 

 popliteal nerves may be involved in the pressure, causing inter- 

 ference with their function, the pain frequently induced being 

 attributed to rheumatism. The popliteal surface of the femur, 

 the posterior ligament on the knee-joint and the upper part of 

 the tibia all come in for their share of pressure, and considerable 

 erosion may occur. 



It must be remembered in connection with a popliteal 

 aneurysm that various swellings which occur in the popliteal 

 space may lie superficial to the artery and obtain thereby 

 communicated pulsation, which without careful differentiation 

 may lead to an error in diagnosis. 



In the treatment of an aneurysm anatomical considerations 

 are of the greatest importance. 



For an aneurysm situated in a limb there can be little doubt 

 that the ideal treatment is to ligature the artery upon which the 

 aneurysm is placed both on the proximal and on the distal sides 

 of the sac, and to dissect out the sac itself. This, however, may 



