83- 



HUMAN ANATOMY. 



Greater sciatic nerve 



Popliteal artery 



Practical Considerations. — The popliteal artery is rarely wounded because 

 of its protected position on the posterior aspect of the limb and in the 'hollow of the 

 ham. Its upper portion is overlapped by the outer border of the semimembranosus^ 

 muscle, and its lower portion by the inner head of the gastrocnemius ; the inter- 

 mediate portion, covered only by skin, fascia, and areolo-fatty tissue, is very deeply 

 placed and is not more than an inch in length. It may be torn in luxation of the 

 knee, or wounded in fracture of the lower end of the femur, or during certain opera- 

 tions, as osteotomy of the femur for genu valgum. Laceration or wound of this 

 vessel is more dangerous than a corresponding injury to the brachial at the bend of 

 the elbow, because of the greater proximity — in the case of the popliteal — of the 

 branches on which the chief anastomotic supply depends ; and because of the 

 unyielding character of the walls of the space in which the efiused blood is confined. 

 Aneurism of the popliteal artery comes next in frequency to aneurism of the 

 thoracic aorta. This is due (^a) to the frequent minor strains occurring during 

 flexion and extension of the knee. If extreme, the former movement bends the 

 artery at such an acute angle that the flow of blood through it is arrested and 



the pressure above this 

 Fig. 735. point greatly increased ; 



and the latter may so 

 stretch the vessel longi- 

 tudinally that if its elasticity 

 is at all diminished by ather- 

 omatous changes the inner 

 and middle coats are 

 thinned or ruptured. (<^) 

 The lack of muscular sup- 

 port which the artery — sur- 

 rounded by loose cellular 

 tissue — receives also favors 

 the development of aneur- 

 ism, (r) The artery is said 

 to be unusually liable to ath- 

 eromatous degeneration, 

 (^) It divides a short dis- 

 tance below into two 

 vessels, thus increasing the 

 blood-pressure above the 

 bifurcation. (^) Its course 

 is curved (like that of 

 the aortic arch), and hence 

 the pressure is irregularly 

 distributed. (_/) The ten- 

 dinous opening in the 

 adductor magnus, through 

 which the vessel runs, con- 

 stricts it slightly at each pulse-beat and tends — as in the case of the abdominal aorta 

 below the hiatus aorticus — to produce a little dilatation below that level. As both 

 these vessels have been said to be especially w^eak in these regions, it may be 

 possible that some trifling but oft-repeated interference with the vasa vasorum 

 favors degenerative changes by slightly diminishing the blood -supply to the vessel 

 walls. 



Aneurism may occur suddenly, with a sensation resembling that produced by a 

 blow with a whip. It may develop slowly, and, if it takes a forward direction, with 

 symptoms simulating rheumatism on account of the pressure upon the posterior 

 ligament of the knee-joint — i.e., dull pain, stiffness, semi-flexion of the knee, inability 

 to extend the joint freely. If it develops in the opposite direction, the absence of 

 resistance causes the early appearance of a characteristic pulsating tumor with bruit 

 and the usual signs of aneurism. It should not be confused with an enlarged bursa 

 (page 647), the subject of transmitted pulsation, or with tumor or abscess overlying 



Semitendinosus 



Semimembranosus 



Gracilis 



Sartorius 



Inner head of 

 gastrocnemius 



Popliteal vein 



Biceps 



Popliteus 



Outer he^d ot 

 gastrocnemius 



External 

 popliteal nerve 



Communicans 

 peronei nerve 



External 

 saphenous nerve 



External 

 saplienous vein 



Dissection of right popliteal regioti, showing 

 relation of vessels and nerves. 



