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A head is the cephalic part of an organism, which usually comprises the eyes, ears, nose and mouth, each of which aid in various sensory functions, such as sight, hearing, smell, and taste. Some very simple animals may not have a head, but many bilaterally symmetric forms do. Heads develop in animals by an evolutionary trend known as cephalization. In bilaterally symmetrical animals, nerve tissues concentrate at the anterior region, forming structures responsible for information processing. Through biological evolution, sense organs and feeding structures also concentrate into the interior region; these collectively form the head.
A typical insect head possesses a pair of antennae; eyes; mandibles, labrum, maxillae and labium (the latter four forming the cluster of "mouth parts"). Lying above the oesophagus is the brain or supraesophageal ganglion, divided into three pairs of ganglia: the protocerebrum, deutocerebrum and tritocerebrum from front to back.
Versus invertebrate chordates
Though invertebrate chordates such as the lancelet have heads, there has been a question of how the vertebrate head, characterized by a bony skull clearly separated from the main body, might have evolved from the head structures of these animals. In 2014, a transient larval tissue of the lancelet was found to be virtually indistinguishable from the neural crest-derived cartilage which forms the vertebrate skull, suggesting that persistence of this tissue and expansion into the entire head space could be a viable evolutionary route to formation of the vertebrate head.
Use in heraldry
Both human and animal heads frequently occur as immobile charges in heraldry. The blazon, or heraldic description, usually states whether an animal's head is couped (as if cut off cleanly at the neck), erased (as if forcibly ripped from the body), or cabossed (turned affronté without any of the neck showing). Human heads are often described in much greater detail, though some of these are identified by name with little or no further description.
Mid-sagittal section of a human skull, by Leonardo da Vinci, c. 1489
Transection of a human head, by Thomas Bartholin, 1673
Nerves of the human head, from Gray's Anatomy, 1858
Patron saints of Zürich, fresco, c. 1400-1425
Heraldic depiction of a bison head cabossed
- Jandzik, D.; Garnett, A. T.; Square, T. A.; Cattell, M. V.; Yu, J. K.; Medeiros, D. M. (2014). "Evolution of the new vertebrate head by co-option of an ancient chordate skeletal tissue". Nature. doi:10.1038/nature14000. For laysummary see: "Evolution: How vertebrates got a head". Research. Nature (paper) 516 (7530): 171. 11 December 2014.
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