**Core Concept:** Poal vein is a term used to describe the venous network formed by the union of several veins in the lower limbs. These veins are part of the deep venous system and play a crucial role in venous blood return from the lower limbs to the heart.

**Why the Correct Answer is Right:** The correct answer, **C**, refers to the union of the **popliteal vein** and the **tibiocalf vein** to form the popliteal vein. The popliteal vein is a key component of the deep venous system in the lower limbs, collecting blood from the posterior tibial and peroneal veins and transporting it to the heart. The tibiocalf vein, on the other hand, is formed by the union of the **tibial vein** and the **calf vein**. The tibial vein receives blood from the anterior tibial vein and the posterior tibial vein, while the calf vein collects blood from the **superficial gastrocnemius vein** and the **deep gastrocnemius vein**.

**Why Each Wrong Option is Incorrect:**

A. This option refers to the **saphenous vein**, which is a superficial vein located in the anterior aspect of the lower leg and does not form part of the deep venous system.

B. This option refers to the **sapheno-femoral junction**, where the saphenous vein and the internal femoral vein join to form the femoral vein, which is not relevant to the formation of the popliteal vein.

D. This option refers to the **femoral vein**, which is a component of the deep venous system but is not involved in the formation of the popliteal vein. The femoral vein collects blood from the inguinal region and joins the internal iliac vein to form the common iliac vein, which eventually empties into the inferior vena cava.

**Clinical Pearl:** A thorough understanding of venous anatomy is essential for clinicians to accurately assess and manage patients with venous insufficiency, deep vein thrombosis, or other venous disorders. Anatomical knowledge helps in identifying the site of involvement and choosing the appropriate treatment modalities.