The atrioventricular (AV) conducting system of the heart was histologically investigated in 14 species in 9 orders of aves. The main part of the AV conducting system in aves was fundamentally similar to that in mammals, but the avian AV bundle was longer than the mammalian one and its left and right limbs had no branches crossing the ventricular cavities. In the avian heart, the accessory part of the AV conducting system was well developed. It consisted of the right AV Purkinje ring, which originated from the AV node, and the recurrent branch, which emanated from thd AV bundle. In general, the former encircled the right AV orifice and the latter encircled the aortic root, together forming an 8-shaped loop. However, the degree of development of the accessory part varied among avian species, hence allowing six types of the accessory part to be distinguished.
The Japanese Society of Veterinary Science