Quantitative studies on the postnatal growth of the spinal cord and the vertebral column of the albino mouse

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Abstract
The rate of growth of the various regions of the spinal cord and the vertebral column of the albino mouse aged, 1, 10, 20, 30 and 120 days was studied. It was found that: There is more rapid growth in the length of the vertebral column than that of the spinal cord. The lower regions of the vertebral column grow more rapidly than the upper regions but the reverse was found in the spinal cord resulting in regression of the spinal cord. The cord ends at one day opposite the fifth sacral vertebra and then receded to the fifth lumbar vertebra till 120 days. The white matter has a more rapid rate of growth in volume than the gray matter. So the process of myelination and the growth of the fibers in diameter exceed the rate of growth of the neurons and their dendrites. The packing density of the neurons is nearly the same in all regions of the cord with the exception of the cervical region which showed less packing density due to more branching of their dendrites. The total number of neurons at each region is fixed from birth till maturity. The thoracic region contains the highest number of neurons followed by the cervical then the lumbar and the least number is in the sacral region.