The line where two surfaces meet Example: This tetrahedron has 6 edges. It can also be the boundary of a plane shape, such as the circumference of a circle.
1 12 thoracic vertebrae in the upper back corresponding to each pair of ribs. 2  5 lumbar vertebrae in the lower back.  5 sacral vertebrae which are fused together to form 1 bone called the sacrum and 4 coccygeal vertebrae that are also fused together to form the coccyx or tailbone.
The_human_spine_has_7_cervical,_12_Thoracic_and_5_Lumbar_vertebrae_as_well_as_5_(fused)_in_the_sacrum_and_another_4_(fused)_in_the_coccyx_which_totals_33. The human spine has 7 cervical, 12 Thoracic and 5 Lumbar vertebrae as well as 5 (fused) in the sacrum and another 4 (fused) in the coccyx which totals 33.lmost all humans are born with 33 separate vertebrae. By adulthood, most have only 24. This is due to the fusion of the vertebrae in certain parts of the spine during normal development.