Passage: Most living vertebrates have pineal glands. It is likely that the common ancestor of all vertebrates had a pair of photosensory organs on the top of its head, similar to the arrangement in modern lampreys. Some extinct Devonian fishes have two parietal foramina in their skulls, suggesting an ancestral bilaterality of parietal eyes. The parietal eye and the pineal gland of living tetrapods are probably the descendants of the left and right parts of this organ, respectively.During embryonic development, the parietal eye and the pineal organ of modern lizards and tuataras form together from a pocket formed in the brain ectoderm. The loss of parietal eyes in many living tetrapods is supported by developmental formation of a paired structure that subsequently fuses into a single pineal gland in developing embryos of turtles, snakes, birds, and mammals.The pineal organs of mammals fall into one of three categories based on shape. Rodents have more structurally-complex pineal glands than other mammals.Crocodilians and some tropical lineages of mammals (some xenarthrans (sloths), pangolins, sirenians (manatees & dugongs), and some marsupials (sugar gliders) have lost both their parietal eye and their pineal organ. Polar mammals, such as walruses and some seals, possess unusually large pineal glands.All amphibians have a pineal organ, but some frogs and toads also have what is called a "frontal organ", which is essentially a parietal eye.Pinealocytes in many non-mammalian vertebrates have a strong resemblance to the photoreceptor cells of the eye. Evidence from morphology and developmental biology suggests that pineal cells possess a common evolutionary ancestor with retinal cells.Pineal cytostructure seems to have evolutionary similarities to the retinal cells of the lateral eyes. Modern birds and reptiles express the phototransducing pigment melanopsin in the pineal gland. Avian pineal glands are thought to act like the suprachiasmatic nucleus in mammals. The structure of the pineal eye in modern lizards and tuatara...

Question: Where are the circadian rhythms sent from in humans and other mammals?
eye