[Comparative anatomy of the spinal cord of semi-aquatic, aquatic and terrestrial mammals].

Skeletotopically, cervical thickening of the spinal cord in semiwater mammals (Callorhinus ursinus, Eumetopias jubatus, Phoca larga, Phoca kurilensis, Enhydra lutris) corresponds to 4--5, and in terrestrial mammals (Ursus arctos, Vulpes vulpes)--to 3--6 cervical vertebrae. Lumbar thickening in terrestrial spicies and in Enhydra lutris is situated more caudally from the thoracic portion than in Phocidae. In a typically water animal (Phocaenoides dalli) the cervical thickening is expressed feebly, the lumbar one is absent, the epidural space is developed better than in terrestrial and semiwater animals. In Phocidae, comparing terrestrial species, bringing together of the nerve fasciculi taking their origin from the spinal cord is observed, a powerful development of a "horse tail", elongation of nerve bands, going from the spinal cord to spinal ganglia. The relative length of the spinal cord in semiwater and water animals is less than in terrestrial ones. It is stated that differences in spinal cord construction and topography of the animals in question are closely connected with their environmental conditions, functional loading and locomotor peculiarities.