Explanation

Ideally, there are as many pairs of spinal nerves as the number of vertebrae. However, in man 31 pairs of spinal nerves are present including 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves and 1 pair of coccygeal nerves. The cervical vertebrae are the vertebrae of neck region. Whether the neck is short as in mouse or long as in a camel or giraffe, their number is seven in all mammals (including man) except some, $e.g.,$ sloths and the sea cows.