Microscopy of the umbilical cord vein and arteries from cross-bred equine in different pregnancy stages was studied. Umbilical cords from 8 fetuses were collected with age varying from 73 to 249 days. For histological study several staining techniques were used, such as hematoxilin-eosin, Verhoeff, Gordon, picrossirius and Masson's Tricrome. Both the arteries and the veins presented a tunic intern in the constitution of their walls that showed a characteristic plaiting mainly in the arteries, a tunic media that contained a well developed musculature, and a tunic adventitia. Reticular fibers were common characteristics in the wall of the umbilical vessels, even so more numerous in the walls of the umbilical veins. On the other hand, the elastic fibers appeared in small amount mainly in the tunic media and adventitia. Finally, the disposition of the collagen fibers could be evidenced by the picrossirius staining technique, and they were very similar in both the vein and the umbilical arteries.
Horse; Umbilical cord; Vein; Artery
