A 49 year old man suffering from carcinoma of prostate was x -rayed. He showed areas of sclerosis and collapse of T 10 and T11 veebrae in x-ray. The spread of this cancer to the above veebrae was through -

Ans is 'c' i.e. Internal veebral plexus of veins Prostatic cancer spreads to the bones through blood vessels; first into Batson's periprostatic venous plexus * and then into the internal veebral plexus of veins. This metastatis is possible because of valveless communication* between the periprostatic and veebral plexus of veins.