The invention relates to a sensor for in vivo measurements comprising a planar substrate, and a sensor shaft bearing several electrodes, and a sensor head for connecting the sensor, wherein the sensor head has metal surfaces as contact fields for contact making, which are connected to the electrodes by way of conductor paths. The sensor head protrudes laterally to the sensor shaft so that the contact fields are arranged laterally from the sensor shaft, whereas the conductor paths extend in parallel on the sensor head transversely to the longitudinal direction of the sensor shaft. Also disclosed is a system having a sensor as just described and a suitable plug connector therefor.