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.
Most babies begin learning to sit up at some time between four months and seven months. Your little one could be sitting well without support by the time sheâs nine months old. Sitting takes your baby a step closer on the road to walking. Sitting usually comes after your baby gets the hang of rolling over and before she learns to crawl. Don't worry if your baby does things in a different order. All babies develop at their own rate and in different ways. To be able to sit by herself, your baby needs to develop strong head and neck muscles.