Embryologically, the pulmonary system arises as an outgrowth of the digestive tract. It begins as a small bud which grows from the ventral part of the pharynx (Fig. 227). The bud increases in length to form the trachea, which in turn divides into right and the left primary bronchi (Fig. 228). The ends of these bronchi continue to grow and divide until eventually a complex bronchial tree with the terminal alveoli is formed. At first, the pleural cavity is in direct communication with the abdominal cavity, the two together forming the celom. Later, these are separated by a transverse partition, the diaphragm.
KeywordsPulmonary Vein Left Lung Phrenic Nerve Pleural Cavity Middle Lobe
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