The circumferential length of the internal elastic membrane measured by computer digitizer morphometry, and its relation to in vivo aorta diameter.

The circumference of the internal elastic membrane of rabbit aorta has been measured by means of computer digitizer morphometry. Measurements were made on sections cut at 90 degrees to the longitudinal axis of the vessel. These measurements were compared with calculated values of a luminal circumference based on in vivo measurements of the external diameter and vessel wall thickness measured on the sections prepared. It is found that the lengths of the internal elastic membranes measured are significantly greater than the calculated values. Thus the internal elastic membranes must be thrown into folds in vivo. The possible function of the folds is considered.