Histological study of the atrioventricular node and bundle in the heart of ovine fetus

This study was conducted on the atrioventricular node (AVN) and atrioventricular bundle (AVB) of five four-month-old ovine fetuses. The histological structure of these components was studied by routine histological techniques and use of specific staining methods. The AVN was caudally located adjacent to the root of the aorta. It was almost spherical in shape and consisted of twisty cells. The node was mainly composed of “P” cells. There were not seen internodal pathways in the heart of four-month ovine fetus. The AVB was a direct continuation of the AVN and it passed through the fibrous ring toward the apex of the interventricular septum. At this place the right bundle branch (RBB) was ramified. The cells of the AVB were wider, shorter and lighter than normal myocardial cells. Some of the bundle cells have been changed to purkinje cells, whereas some others still did not represent typical characteristics of purkinje cells.