Each cerebral hemisphere is divided into four lobes; the frontal, parietal, temporal, and the occipital. The Frontal Lobe is the most anterior lobe of the brain.Its posterior boundary is the fissure of Rolando, or central sulcus, which separates it from the parietal lobe.Inferiorly, it is divided from the temporal lobe by the fissure of Sylvius which is also called the lateral fissure.he Frontal Lobe is the most anterior lobe of the brain. Its posterior boundary is the fissure of Rolando, or central sulcus, which separates it from the parietal lobe. Inferiorly, it is divided from the temporal lobe by the fissure of Sylvius which is also called the lateral fissure.
Main article: Thoracic diaphragm. The diaphragm is the major muscle responsible for breathing. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, so that its centre moves caudally (downward) and its edges move rostrally (upward).
The muscles that contribute to quiet breathing are the external intercostal muscles and the diaphragm. (The external and internal intercostals are the muscles that fill the gaps between the ribs.) When drawing breath (i.e., during inspiration), the external intercostal muscles and diaphragm contract simultaneously.