The vertebral venous plexus is a vascular network that runs from the cervical to sacral vertebral canal in the spine of mammals. The objective of this study was to perform an anatomical study of the internal vertebral venous plexus (IVVP) in horses. The spine of five horse specimens (four adults and one foal) was dissected for morphological analysis of the IVVP. The IVVP was observed in the ventral epidural space of the vertebral canal and was composed by two symmetrical longitudinal veins. There was a difference in the IVVP diameter and morphology between foal and adult horses. In all the specimens, the IVVP was more developed at cervical segments, while a decrease in the IVVP diameter was seen in sacral and caudal segments. The cervical IVVP communicated cranially with the basilar, interbasilar and sigmoid sinuses. Transverse communicating branches between left and right IVVP were occasionally observed at the cervical, sacral and caudal vertebral segments. In conclusion, the IVVP in horses is similar to other domestic animals, has transverse connections and is more developed at cervical segment. The diameter of the longitudinal veins decreased and at the caudal segment reaches its thinnest development.
KEY WORDS: Veins; Internal vertebral venous plexus; Horses; Anatomy.