Fig. 2. Midwife's or obstetrician's ‘eye’ view of a neonatal head passing through the birth canal. In each drawing, the maternal pelvis and neonatal head are shown in inferior view, with the sacrum at the bottom of the picture and the pubic symphysis at the top. The relative dimension of the head and the pelvis at each position is to be noted. In great apes, unconstrained birth; in australopithecines and human, constrained birth. (Pan is chimpanzee, A.L 288-1 is Lucy, an australopithecine, Homo is human). (Reprinted with permission from John Wiley and Sons).