Comparative Skeletotopy of the Mammalian Lumbar Spinal Cord

The spinal cord is the most phylogenetically ancient partof the central nervous system. Due to a faster growth of the spinalcolumn relative to the spinal cord in ontogenesis, some spinal segmentsin adult mammals are shifted rostrally relative to the eponymousvertebrae, which is called the ascent of the spinal cord. Basedon the literature data, the skeletotopy of the lumbar spinal cordwas compared in 17 mammalian species, while in 4 of them, it wasadditionally compared in newborn and adult animals. The length ratioof the L2 segment and VL2 vertebra, as well as the number of thevertebra that encloses the 29th spinal segment, were determinedas measures characterizing the degree of spinal cord ascent. Basedon the literature data, digital dexterity and the encephalizationquotient were also determined as measures frequently used in comparativestudies. It was shown that different species differ to a greater extentin the relative length of the rostral lumbar segments, whereas withinthe same species, newborns differ from adults in the relative lengthof the caudal lumbar segments. In most species, the degree of spinalcord ascent positively correlates with digital dexterity and theencephalization quotient. The above-mentioned macroanatomical characteristicsof the spinal cord may be used to analyze the relationships betweenadaptive mechanisms in various mammalian species.