476 SURGICAL APPLIED ANATOMY, [dhap. xxi. 



artery is more frequently the seat of aneurism than is 

 any other artery in the body, save only the thoracic 

 aorta. In 551 cases of spontaneous aneurism, col- 

 lected by Crisp, the popliteal vessel was the seat of the 

 disease in 137 instances, the thoracic aorta having 

 been affected in 175 of the cases. This marked 

 disposition to aneurism depends upon many factors. 

 The vessel is subjected to a great deal of movement, 

 and often to very violent movement. Experiments 

 upon the dead body show that the inner and middle 

 coats of the vessel may be ruptured by extreme 

 flexion of the knee, and that a like rupture may in a 

 smaller percentage of cases be brought about by 

 forcible extension. Moreover, except when the limb 

 is in the position of extension the nopliteal artery is, 

 like the thoracic aorta, much curved. Then, again, 

 the vessel breaks up into two large vessels, and it is 

 well known that the point of bifurcation of an artery 

 is a favourite spot for aneurism. Lastly, the artery is 

 supported only by the lax tissue of the popliteal space, 

 and the support of strong muscles given elsewhere 

 to so many large vessels is practically absent. Some 

 popliteal aneurisms have been successfully treated by 

 flexing the knee and retaining the limb for some time 

 in that position. That flexion can have a direct effect 

 upon the lumen of the vessel is shown by the dimi- 

 nished pulse at the inner ankle produced by forcibly 

 bending the leg upon the thigh. The artery and vein 

 are so adherent that it is difficult to separate the two 

 when applying a ligature to the arterial trunk. This 

 adhesion must have been appreciated by any who 

 have taken pains to " clean " the artery in a dissection 

 of the ham. 



The popliteal vein is a remarkably substantial 

 vessel, and has walls so dense and thick, that on 

 section they often look more like the tunics of an 

 artery. On the ground of this peculiarity, and of 



