On the edge of Mexico City's famed Zócalo plaza, next to the ruins of the Aztec sacred pyramid known as the Templo Mayor, the remains of an animal—perhaps a dog or a wolf—were discovered.

Hygiene and ritual marked every moment of life for pregnant Aztec women. The tlamatlquiticitl—midwife—offered those in her charge a remarkable 16th-century birthing plan, combining practical ...