MRI-based brain volumetrics is an established methodology of great versatility and reliability with a broad range of potential applications in medicine and basic human brain science. We consider here, more theoretical implications of brain tissue volumes. Specifically, we suggest that volume is an evolutionarily and developmentally regulated fundamental property of tissue, in this instance the brain and its component structures. Within this framework (1), regularities in relative variation of volumes with respect to mean volume of a structure are viewed as systematic manifestations of the rules of histogenetic process (2), regularities in the relative strength of correlation of volumes of structures are suggested to reflect constraints which serve systematically the requirements of neural systems operation. These hypotheses, if supported by extensive observation, may guide the design of applications of MRI based volumetric analysis of the human brain.