THE LOWER LIMB 443 



irticulation, where it divides into branches. These anastomose with 

 the following arteries : (i) superior external articular ; (2) inferior 

 internal articular ; (3) anterior tibial recurrent ; and (4) posterior 

 tibial recurrent (inconstant). 



The inferior internal articular artery courses at first obliquely 

 downwards and inwards along the upper border of the popliteus 

 muscle, and then passes inwards below the level of the internal 

 tuberosity of the tibia, where it lies beneath the internal lateral 

 ligament of the knee-joint. On reaching the inner side of the 

 articulation, it divides into branches which anastomose with the 

 following arteries: (i) superficial branch of the anastomotica 

 magna ; (2) superior internal articular ; (3) inferior external articu- 

 lar ; (4) anterior tibial recurrent ; and (5) posterior tibial recurrent 

 (inconstant). 



Varieties of Popliteal Artery. — i. The vessel may divide into its anterior 

 and posterior tibial branches at the upper border of the popliteus muscle. 



2. The terminal branches may be three in number instead of two, the 

 additional branch being the peroneal artery. 



3. In very rare cases the popliteal arterj- divides high up into two branches 

 of equal size, which subsequently unite prior to the normal termination of the 

 vessel. 



Popliteal Vein. — ^This vessel commences at the lower border of the 

 popliteus muscle, where it is formed by the union of the venae 

 comites of the anterior and f)Osterior tibial arteries, and it termi- 

 nates at the posterior margin of the femoral opening, which is in 

 connection with the adductor magnus, where it becomes the femoral 

 vein. The relations of the vessel have already been described. Its 

 tributaries correspond with the branches of the pophteal artery, 

 with the addition of the external or short saphenous vein. 



Internal Popliteal (Tibial) Nerve. — ^This nerve is one of the ter- 

 minal branches of the great sciatic, and it derives its fibres from 

 the ventral divisions of the descending branch of the fourth lumbar, 

 the fifth lumbar, the first and second sacral, and the upper branch 

 of the third sacral ner\'es. It extends from the superior angle of 

 the pophteal space to the lower border of the pophteus muscle, 

 where it becomes the posterior tibial nerve. The relations. of this 

 nerve have been given in connection with the popliteal artery. 

 Branches. — ^The branches are articular, cutaneous, and muscular. 

 The articular branches are three in number (sometimes two), 

 as follows : superior (inconstant), accompanj.'ing the superior 

 internal articular artery ; central or azygos, going with the corre- 

 sponding artery ; and inferior, accompanying the inferior internal 

 articular artery. 



. The cutaneous branch is called the ramus communicans tibialis. 

 I It descends in the middle line beneath the deep fascia as far 

 as the centre of the calf. Here it pierces the deep fascia, and 

 shortly after\vards it is joined by the ramus communicans fibularis 

 ; from the external popliteal. In this manner the external or short 

 1 saphenous nerve is formed. 



