An extracorporeal circuit has been conceived including: lines (16) which include passages for blood or a medical liquid； a connector (38, 40) at a free end of each of the lines (16)； a cassette (18) supporting the lines, and dummy connectors (42, 44) attached to the cassette (18) and each adapted to form a mating connection with a respective one of the connectors (38, 40) at the free ends of the lines (16), wherein the connectors (38, 40) are arranged in accordance with a sequence in which the lines (16) are attached for a blood treatment session or are grouped in accordance with types of liquids to flow through the lines (16) during the blood treatment session. The extracorporeal circuit may be a circuit for dialysis and the circuit includes a hemodialyzer. Further, the connectors (38, 40) and dummy connectors (42, 44) may each be one of a male or female luer lock connector, and the dummy connectors (42, 44) may include both male and female connectors.
