62 



POPLITEAL REGION AND ARTERY. 



femur, and is of sufficient breadth, at this its 

 lower part, to extend beyond either side of the 

 tendon of the former muscle, thus contracting 

 the lateral dimensions of the bottom of this 

 space by encroaching within it. The long head 

 of the biceps, leaving the former muscles, de- 

 scends obliquely to cross the outer origin of the 

 gastrocnemius by its strong tendon, which is 

 subsequently implanted into the head of the 

 fibula; it receives, as it descends, the thick 

 fleshy mass of its shorter portion, which assists 

 the semimembranosus in narrowing the bottom 

 of the popliteal space, shutting it in also exter- 

 nally and above, by its attachment to the linea 

 aspera as low as the outer condyle. The supe- 

 rior angle of this space is formed at the point of 

 divergence of these hamstring muscles, and the 

 lateral angles are occasioned by their crossing 

 the heads of the gastrocnemius ; this latter 

 muscle is attached to either condyle of the 

 femur by its two heads, the internal being the 

 longer and larger ; they converge to unite in 

 the median line a little below the knee-joint : 

 these origins have each a bnrsa interposed be- 

 tween them and the condyle ; the little fleshy 

 belly of the plantaris muscle accompanies the 

 outer head and lies beneath it ; by their union 

 the inferior angle of the popliteal region is pro- 

 duced. At the bottom of the space we meet 

 with, first, the posterior, flat, triangular surface 

 of the femur, and, secondly, the back part of the 

 knee-joint strengthened by its posterior liga- 

 ment (the ligament of Winslow). This struc- 

 ture is derived from the tendon of the semi- 

 membranosus ; it insinuates itself beneath the 

 inner head of the gastrocnemius, and, forming 

 a flat and dense tendinous aponeurosis, extends 

 across the back of the joint to the external con- 

 dyle, adhering to the synovial membrane ; there 

 are several small openings in it, produced by a 

 separation of its fibres, for the passage of vessels 

 to the interior of the articulation : lastly, the 

 popliteus muscle, which is flat, triangular, and 

 situate behind and below the joint, begins, by 

 a round tendon, from the outer condyle and 

 spreads out by muscular fibres upon the poste- 

 rior surface of the tibia to be inserted into its 

 oblique ridge. 



On removing the fascia, two large nerves are 

 seen to traverse the popliteal space, and are in- 

 differently called the internal popliteal or tibial, 

 and the external popliteal or peroneal nerves ; 

 they are the terminal branches of the sciatic, 

 which nerve generally bifurcates at the upper 

 angle of this region : the point of division, how- 

 ever, is very variable, sometimes occurring even 

 within the cavity of the pelvis, in which case, as 

 the two nerves emerge, they are usually sepa- 

 rated by a slip of the pyriformis muscle ; com- 

 monly a very trifling dissection will affect their 

 separation some distance up the thigh. The 

 internal popliteal or tibial nerve is the larger of 

 the two, and appears to be the continuation of 

 the sciatic ; it takes a nearly perpendicular 

 course through the popliteal space in the middle 

 line, and will be found at first to lie almost im- 

 mediately beneath the fascia, a small quantity 

 of fat intervening ; it dips more deeply into the 

 space as it descends, passes between the heads 



of the gastrocnemius and over the popliteus 

 muscle, and, insinuating itself beneath the ten- 

 dinous arch of the soleus, courses down the 

 back of the leg under the name of posterior 

 tibial. Owing to the oblique direction which 

 the popliteal artery follows, this nerve alters its 

 relation to it at different parts of its course ; 

 until they reach the bend of the knee, the nerve 

 is a little distance to the outer side of the artery, 

 but superficial or posterior, and separated from 

 it by a thick layer of adipose tissue : at the 

 joint, the nerve is still posterior to,but in closer 

 relation with it, and subsequently upon the 

 popliteus muscle crosses the artery to gain its 

 inner side. About the centre of the popliteal 

 space, the tibial nerve sends off a small branch 

 called the communicans tibialis, which descends 

 superficially between the heads of the gastro- 

 cnemius,and is afterwards concealed in agroove 

 formed by their union ; it perforates, at a va- 

 riable point, the aponeurosis of the leg, and, de- 

 scending towards the outer malleolus, is joined 

 a little above it by the communicans peronei, a 

 branch of the peroneal nerve ; thus reinforced, 

 it is increased in size, and, accompanied by the 

 posterior saphena vein, winds behind the outer 

 ankle to be continued along the outer side of the 

 foot. To return to the internal popliteal nerve, 

 which sends off, while crossing the back of the 

 joint, four or five other branches for distribu- 

 tion to the gastrocnemii and plantaris muscles, 

 and also furnishes some articular twigs ; these 

 are all accompanied by corresponding branches 

 of the popliteal artery, and from their situation 

 are liable to be compressed by an aneurismal 

 tumour. The external popliteal or peroneal 

 nerve descends along the inner side of the bi- 

 ceps muscle, by which it is guided to the head 

 of the fibula, and winds round the neck of that 

 bone beneath the peroneus longus muscle to 

 divide into its terminal branches ; in the 

 ham it gives off the small branch called the 

 communicans peronei. This will be seen to de- 

 scend over the outer head of the gastrocnemius 

 muscle and beneath the fascia, and, piercing 

 the aponeurosis of the leg at a very variable 

 distance above the outer angle, joins the com- 

 municans tibialis ; it presents frequent varieties 

 both with regard to its size and the point of 

 junction with the last-named nerve : occasion- 

 ally the union occurs in the popliteal space. 

 To reach the popliteal vessels, a quantity of fat 

 which fills up this space must be dissected 

 out : it is very abundant, and surrounds and 

 supports the popliteal artery. 



THE POPLITEAL ARTERY is simply a conti- 

 nuation of the femoral, and is so named immedi- 

 ately after the latter vessel has passed through 

 the elliptical aperture of the adductor muscles ; 

 this opening is bounded above by the united 

 tendons of the adductor longus and adductor 

 magnus muscles ; inferiorly, by the union of the 

 vastus internus tendon with that from the ad- 

 ductor magnus which descends to the inner 

 condyle ; externally, by the tendon of the vastus 

 internus, and internally, by that of the adductor 

 magnus. Passing through this tendinous aper- 

 ture, the artery is at first situated on the inner 

 side of the femur at the junction of its middle 



