Inductive definition of CW complexes. If the largest dimension of any of the cells is n, then the CW complex is said to have dimension n. If there is no bound to the cell dimensions then it is said to be infinite-dimensional. The n-skeleton of a CW complex is the union of the cells whose dimension is at most n.
Deoxygenated blood enters the right atrium through three major veins: the superior and inferior vena cava and the coronary sinus. The superior vena cava returns all of the blood to the heart from tissues superior to the heart in the head, neck, arms and upper thorax.
1 The pulmonary veins carry oxygenated blood from the lungs into the left atrium where it is returned to systemic circulation.  The aorta is the largest artery in the body. It carries oxygenated blood from the left ventricle of the heart into systemic circulation.