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.
The venae cavae (from the Latin for hollow veins, singular vena cava) are two large veins (venous trunks) that return deoxygenated blood from the body into the heart. In humans there are the superior vena cava and the inferior vena cava, and both empty into the right atrium.