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.
Knowing what to look for and how to help your baby learn to sit on her own is important. Your baby might start sitting as early as 4 months old or as late as 9 months. Don't try to rush it. According to pediatrician, Dr. Kurt Heyrman, you should make sure she has some specific large motor skills such as she should be able to hold her neck up, have some balance, and have trunk muscles.