either of two large organs lying within the chest cavity on either side of the heart; they supply the blood with oxygen inhaled from the outside air and dispose of waste carbon dioxide in the exhaled air, as a part of the process known as respiration.
Most babies first pull themselves up to a standing position between about eight months and 10 months. At this stage your baby will need to hang on to you or a solid piece of furniture. By 11 months she may be able to stand on her own.
Some perfectly normal children don't walk until they're 16 or 17 months old. During her first year, your baby is busy developing coordination and muscle strength in every part of her body. She'll learn to sit, roll over, and crawl before moving on to pulling up and standing at about 9 months.