Epidural vein of the Baikal seal (Pusa sibirica, Phocidae)

The aim of this study was to investigate the anatomical features of the epidural vein of the Baikal seal. The research was conducted at the Department of Animal Morphology and Veterinary Sanitation of the Irkutsk State Agrarian University. The objects of the study were Baikal seals of different ages: newborn seals (n = 4); yearlings (n = 10, up to 1-year-old), immature individuals (n = 10, from 1 year to 4 years old); sexually mature individuals (n = 10, over 4 years old). The seals were caught using large-mesh nylon nets under permits for harvesting for scientific research purposes. The study used anatomical, morphometric and statistical methods. The epidural vein of the Baikal seal lies in the spinal canal from the foramen magnum to the caudal vertebrae. The length of the epidural vein of the newborn Baikal seal was 27.15 ± 2.25 cm, in yearlings – 45.19 ± 1.00 cm, in immature seals – 57.0 ± 1.53 cm, in mature seals – 73.02 ± 1.94 cm. The width of the studied vessel was 0.95 ± 0.06 cm in newborns, 1.29 ± 0.04 cm in yearlings, 1.74 ± 0.05 cm in immature seals, 1.90 ± 0.05 cm in mature seals, and the thickness was 0.18 ± 0.01 cm, 0.43 ± 0.01 cm, 0.54 ± 0.02 cm, 0.83 ± 0.02 cm, respectively. A number of anatomical features of the epidural vein of the Baikal vein have been identified. In the cervical spine, it surrounds the spinal cord dorsally and ventrally just under the vertebral arches, and in other parts of the spinal column, it is located dorsally above it. The epidural vein anastomoses in the cervical region with the dorsal venous collector, and in the thoracic region with the azygos vein and the ventrolateral collector. At the level between the last lumbar and sacral vertebrae, the epidural vein anastomoses with the caudal venous collector of the abdominal wall muscles, which gives blood to the right or left trunk of the caudal vena cava of the corresponding side. In the Baikal seal, the veins of the caudal collector of the abdominal wall muscles do not anastomose with the renal venous plexus.