The Human Body

Pineal Body

Pineal Body is a small, cone-shaped projection from the top of the midbrain of most vertebrates, arising embryologically as an outgrowth of the brain. The pineal body is absent in crocodiles and in mammals of the order Xenarthra (anteaters, sloths, armadillos) and consists of only a few cells in whales and elephants. In humans the structure develops until the seventh year, when it is slightly larger than a pea; thereafter, throughout life, small mineral particles, particularly calcium, may be deposited in the pineal body. The mineral deposits can sometimes be seen in skull X-ray photographs.

The functions of the pineal gland are only beginning to be understood. It has both neural and endocrine properties, and in simple vertebrates such as the lamprey the organ is mounted on a stalk close to an opening in the skull and functions as a photoreceptive organ. Photoreceptive structures linked with the pineal body are still observed in higher vertebrates such as reptiles and even some species of birds. In mammals the pineal body is not light-sensitive, but a neural connection remains between the eyes and the gland. Thus the functions of the pineal body in an animal are linked with surrounding light levels.