The vertebral column, the pectoral girdle and the pelvic girdle form a framework which can support the bulk of the body weight. In a four legged mammal, the vertebral column is supported at two points, the fore and hind limbs, with most of the body weight suspended between them.
The column is arched dorsally between the fore and hind limbs. The body weight acting on this arch tends to
• Force the vertebrae together on the ventral surface. As a result, the centra of the vertebrae are under compression;
• Force the vertebra apart on the dorsal surface. As a result , the muscles and ligaments holding the vertebrae together are under tension.
The centra, muscles and ligaments are built to withstand the above forces.
The body weight on the arch also tends to push the pectoral and pelvic girdles outwards. This is prevented by
• The abdominal arrangement of muscles which resist the forces pushing the girdles apart , and
• The tension in the muscles on the dorsal surface of the vertebral column.
Note : As the body weight is not eventually distributed along the vertebral column, the vertebrae in the different body regions are modified for the functions required in each region. For example, the lumbar vertebrae are the most massive with large centra, as they have to support the most body weight and stress due to locomotion.
The weight of the Heat results in
• The centra of the cervical vertebrae being under compression, and
• The dorsal muscles between the thoracic and cervical vertebrae, and between the cervical vertebrae and the back of the skull, being under tension. ( These two sets of muscled serve to 'hold up' the neck and head respectively.)
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