as labor progresses. This differs in non-human primates as there is no need for neonatal rotation in non-human primates because the birth canal is wide enough to accommodate the infant. This elaborate mechanism of labor, which requires a constant readjustment of the fetal head in relation to the bony pelvis (and which may vary somewhat depending on the shape of the pelvis in question), is completely different from the obstetrical mechanics of the other higher primates whose infants generally drop through the pelvis without any rotation or realignment. In contrast to the narrow shoulders of monkeys and higher primates, which are able to pass through the birth canal without any rotation, modern humans have broad, rigid shoulders, which generally require the same series of rotations that the head undergoes in order to travel through. Due to the evolution of bipedalism in humans, the pelvis had evolved to have a shorter, more forward curved ilium and broader sacrum in order to support ambulating on two legs. This caused the birth canal to shrink and form a more oval shape, thus the infant must undergo specific movements to rotate itself in a certain position to be able to pass through the pelvis. These movements are referred as the seven cardinal movements, which the infant rotates itself at the widest diameter of the pelvis to allow for the narrowest aspect of the fetal body to alight with the narrowest diameter of the pelvic. These movements include engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion. Engagement is the first movement of labor where the first part of the head enters the pelvic inlet. Descent refers to the deeper movement of the head through the pelvic inlet with the widest diameter of the infant's head. Flexion occurs during descent, where tissues of the pelvis create resistance as the head moves down the pelvic cavity and brings the infant's chin to the chest. This allows for the smallest part of the head to begin to push through pelvis and actively promote delivery of the baby. Internal rotation occurs when the head continues to descend and comes in contact with the pelvic floor, which has resistant muscles. These muscles allow for the infant to rotate their head to allow their head and shoulders to move through the pelvic. Due to the broad shape of the sacrum, the head of the fetus must be rotated from