Models of anticausal systems have provided useful means for the analysis and understanding of system performance and properties and found applications in circuits, signal processing and dynamical systems. In this paper, structure and properties of linear time varying (LTV) mixed causal and anticausal systems are studied and state space realizations of cascaded LTV mixed causal and anticausal systems are presented. The conditions for the cascaded system realizations are related to time-varying Sylvester equations in terms of state-space matrices of the systems.