ABSTRACT
The internal morphology of the right and left atria of rabbit, cat, pig, and human, particularly on the luminal structures of the auricle, were observed by stereomicroscope improving corrosion casting method using latex. Structures of the right auricular casts markedly differ from those of the left side, consisting of defined surface sturctures with distinct folds and branching patterns. The main atrial region consists of smooth surfaced single mass of the latex, and the auricular region is characterized by well developed branching patte and delicate small folds. The results of this study indicate that auricula have well organized duct-like luminal structures and many small pouches (out-pocketings) expanding the internal wall of the duct-like structures and small pouches. The endocardial nuclear imprints on the surface of the folds in the auricular region appeared larger and deeper than those on the atrium proper region of the atrial cast. These morphological observation will be aid in understanding structures of auricular lumen, regional differences of the endocardium and their function to the secretory process of atrial natriuretic peptide (ANP) release.