Figure 2-2
Basic structure and position of the diaphragm.

• Bilateral muscles inserting on a "central (nonmuscular) tendon".
• Originates on the lower six ribs and lumbar vertebrae.
• Motor innervation from ventral rami C3, C4 and C5 (phrenic nerve).
• Separates the thoracic and abdominal cavities.
• Increases thoracic cage volume without rib movement. (Figure 2-2)

The bone and muscle combination making up the wall of the thoracic cage is very strong. It is able to withstand the negative pressures of respiration while protecting the vital organs it contains.