Complex sentence: Elsevier; 7th ed. Interstitial matrix is present between various cells (ie. in the intercellular spaces) whereas basement membranes are sheet-like depositions of ECM on which various epithelial cells rest.
Split into simpler sentences: Elsevier; 7th ed. Interstitial matrix is present between various cells (i.e., in the intercellular spaces). Basement membranes are sheet-like depositions of ECM on which various epithelial cells rest.