en Original Original <p dir="ltr" style="text-align: justify;"><strong>Introduction:</strong> We did this study because there were a few studies about aorto-branch junction.<br> <strong>Methods:</strong> Four light microscope and electron microscope study, the abdominal aorta, renal&nbsp;artery, and the adjoining right and left renal arteries were dissected out from 4 neonate dogs.<br> <strong>Results:</strong> Based on the results, there is only one cell type in the tunica intima of endothelium in&nbsp;both arteries. In abdominal aorta, there were open connective tissue spaces, containing elastic&nbsp;fibers between the internal elastic membrane and endothelium. In renal artery, endothelial cells&nbsp;were attached directly to the internal elastic membrane. In the abdominal aorta tunica media,&nbsp;layers of smooth muscle cells alternating with elastic lamellae were observed, but in renal&nbsp;artery, the smooth muscle cells were close to each other and a small quantity of collagen and&nbsp;elastic fibers were found between them. There were more dense bodies in the renal artery&nbsp;smooth muscle cells compared to the abdominal aorta. The adventitia of the both arteries&nbsp;consisted of scattered fibroblasts and elastic fibers in tunica adventitia of renal artery were more&nbsp;than those in abdominal aorta. There were 2 orientations of smooth muscle cells at the junction&nbsp;of renal artery; circular form in tunica media and longitudinal form in the outer part of tunica&nbsp;media and tunica adventitia and it was similar to the structure of muscular veins.<br> <strong>Conclusion:</strong> aorta and renal artery in neonate dogs show some differences. These differences&nbsp;presumably reflect adaptation to the function of these 2 arteries.</p> Elastic fibers, Collagen, Smooth muscle cell, Dog, Junction 33 38 http://anatomyjournal.ir/browse.php?a_code=A-10-126-1&slc_lang=en&sid=1 Fatemeh Ramezani Nowrozani parsroz@yahoo.com 10031947532846003476 10031947532846003476 Yes Department of Anatomical Sciences, School of Veterinary Medicine, Kazerun Branch, Islamic Azad Univercity, Kazerun, Iran.