canalicular period

canalicular period,

the period or phase of prenatal lung development lasting in different parts of the lungs from the sixteenth or seventeenth week to the twenty-sixth week or later and followed by the terminal saccular period. Basic structures of the gas-exchanging parts of the lungs form and become vascular, and primordial alveoli called the terminal saccules begin to form, enabling respiration to begin. Fetuses delivered after respiration begins may be viable. Also called canalicular phase.