Eye anatomy. Medieval manuscript page illustrating the anatomy of the human eye. The diagram at bottom shows the seven tunicas (layers) and three humours (fluids) of the eye according to the knowledge of the time. This manuscript is from a document known as the 'Book of Macharias', dating from the last quarter of the 14th century or 1st quarter of the 15th century. The text is in Latin. It is thought to be connected with a 12th-century treatise by an author named Zacharias.