Comparative Skeletotopy of the Mammalian Lumbar Spinal Cord

Abstract

The spinal cord is the most phylogenetically ancient part of the central nervous system. Due to a faster growth of the spinal column relative to the spinal cord in ontogenesis, some spinal segments in adult mammals are shifted rostrally relative to the eponymous vertebrae, which is called the ascent of the spinal cord. Based on the literature data, the skeletotopy of the lumbar spinal cord was compared in 17 mammalian species, while in 4 of them, it was additionally compared in newborn and adult animals. The length ratio of the L2 segment and VL2 vertebra, as well as the number of the vertebra that encloses the 29th spinal segment, were determined as measures characterizing the degree of spinal cord ascent. Based on the literature data, digital dexterity and the encephalization quotient were also determined as measures frequently used in comparative studies. It was shown that different species differ to a greater extent in the relative length of the rostral lumbar segments, whereas within the same species, newborns differ from adults in the relative length of the caudal lumbar segments. In most species, the degree of spinal cord ascent positively correlates with digital dexterity and the encephalization quotient. The above-mentioned macroanatomical characteristics of the spinal cord may be used to analyze the relationships between adaptive mechanisms in various mammalian species.