The purpose of this investigation was to evaluate the functional relationship between the volume and the size of the orifice of small saccular aneurysms such as those found intracranially. There is reason to believe that the relationship between those individual values plays an important,though as yet undefined, part in intra-aneurysmal hemodynamics. Little note is made in the literature of interior aneurysmal measurements save as depicted in drawings or arteriographically. While arteriorgraphy is of value in estimating aneurysmal volume in the functioning state, it has been somewhat less effective in outlining the orifice. An experimental entry to the problem seemed advisable, and this is a report of experience with 21 experimental aneurysms, each of which had a different chamber-volume to orifice-area relationship as expressed mathematically by V/A. Their patency or subsequent thrombosis was evaluated with reference to that quotient.