A cavum septi pellucidi continuous with a cavum Vergae, of the noncommunicating type, was found in a human brain and is described in detail. Out of 89 brains that were examined, a cavum septi pellucidi was present in 16 brains, an incidence of 17.97%; the cavum septi pellucidi and cavum Vergae were both in one brain, an incidence of 1.12%. The cavum Vergae never occurred alone in any of the specimens studied. A review of the literature is made and the following concepts are advanced: 4 types of cava are suggested, including the noncommunicating form which, anatomically, is the typical cavum; these noncommunicating cavities contain cerebrospinal fluid that filters through the septal laminae and is reabsorbed by capillaries and veins of the septa. The main aspects regarding the anatomy, histology and embryology of these cavities is reviewed. The cavum septi pellucidi and the cavum Vergae occur undetected in many instances, and when they are apparent it is because they are part of a wide spectrum of defects in the central nervous system and in other organ systems. At present, the existence and diagnostic significance of these ventricular cavities is becoming recognized by modern procedures, such as computed tomographic scanning.