Ans. is 'c' i.e., Batsons venous plexus o Three principal groups of veins are involved in the venous drainage of the thoracic wall and the breast:1) Perforating branches of the internal thoracic vein,2) Tributaries of the axillary vein, and3) Perforating branches of posterior intercostal veins.o Metastatic emboli traveling through any of these venous routes will pass through the venous return to the heart and then be stopped as they reach the capillary bed of the lungs, providing a direct venous route for metastasis of breast carcinoma to the lungs.o The vertebral plexus of veins (Batson's plexus) may provide a second route for metastasis of breast carcinoma via veins. This venous plexus surrounds the vertebrae and extends from the base of the skull to the sacrum. Venous channels exist between this plexus and veins associated with thoracic, abdominal, and pelvic organs. These vessels provide a route for metastatis emboli to reach the skull, vertebrae, ribs, pelvic bones, and central nervous systemo Metastasis of breast cancer to bone, and especially to thoracic vertebrae, is common due to the direct connection between the intercostal veins draining the breast and the internal vertebral plexus also known as Batson's plexus. In 1940 Batson found that dye injected into the breast of female specimens could be recovered in the vertebral veins.