Veins are the blood vessels which carry oxygen depleted blood from the peripheries and end organs of the body. These blood vessels appear bluish due to the oxygen depleted nature of the blood and will consist of a thin wall than its arterial counterpart.
The lower limb can be considered unique in its blood circulation as it is the most dependant part of the human body. Due to its dependency, an enormous amount of work needs to be done in order to take the used up blood towards the heart. Thus, the transport of blood within the veins of the lower limb would be most often against the gravity. But, the venous system of the lower limbs are developed in such a way that it would make use of muscle contractions in the vicinity as well as the pressure maintained in the arterioles for the push towards the heart. Further, the presence of a valve system which will allow blood to flow only towards the heart will prevent the blood from flowing back along the gravitational effect.
When considering the venous drainage of the lower limb, there are two major blood vessels that need mentioning. These are the long or the great saphenous vein and the short or the small saphenous vein.
The start of these blood vessels takes place from the venous network of the foot and it can be simply stated that, the two veins are derived from either end of this network.
The long saphenous vein will ascend anterior to the medial malleolus of the ankle and will readily ascend in the anterior part of the lower limb. It will further ascend behind the medial condyle of the femur and will traverse the saphenous opening of the fascia lata. Thereafter, it will drain in to the femoral vein for the rest of the journey.
The small saphenous vein will pass through posteriorly to the lateral malleolus of the ankle and would ascend posteriorly along the lateral border of the calcaneal tendon and will penetrate the deep fascia after inclining to the middle of the fibulae. Following this, the short saphenous will ascend between the heads of the gastrocnemius muscle and would drain in to the popliteal vein in the popliteal fossa.
Both long saphenous and the sort saphenous will have many anastomoses between them before draining on to the major veins.
Apart from these, it should also be noted that, there are several penetrating veins that link the superficial and deep veins and thereby facilitating the blood to be diverted from the superficial to the deep branches to make use of the muscle contractions during such times.