Heads develop in animals by anevolutionary trend known ascephalization. Inbilaterally symmetrical animals,nervous tissue concentrate at theanterior region, forming structures responsible for information processing. Through biological evolution,sense organs and feeding structures also concentrate into the anterior region; these collectively form the head.
Sculptures of human heads are generally based on askeletal structure that consists of a cranium,jawbone, andcheekbone. Though the number of muscles making up the face is generally consistent between sculptures, the shape of the muscles varies widely based on the function, development, and expressions reflected on the faces of the subjects.[2]
Proponents ofidentism believe that the mind is identical to the brain. PhilosopherJohn Searle asserts his identist beliefs, stating "thebrain is the only thing in the human head". Similarly, Dr.Henry Bennet-Clark has stated that the head encloses billions of "miniagents and microagents (with no single Boss)".[3]
A typical insect head is composed of eyes,antennae, and components of mouth. As these components differ substantially from insect to insect, they form important identification links. Eyes in the head found, in several types of insects, are in the form of a pair ofcompound eyes with multiple faces. In many other types of insects, the compound eyes are seen in a "single facet or group of single facets". In some cases, the eyes may be seen as marks on thedorsal or located near or toward the head, two or threeocelli (single faceted organs).[5]
Antennae on the insect's head is found in the form of segmented attachments, in pairs, that are usually located between the eyes. These are in varying shapes and sizes, in the form of filaments or in different enlarged or clubbed form.[5]
Insects have mouth parts in various shapes depending on their feeding habits.Labrum is the "upper lip" which is in the front area of the head and is the most exterior part. A pair of mandibles is found on the backside of the labrum flanking the side of the mouth, succeeded by a pair ofmaxillae each of which is known asmaxilliary palp. At the back side of the mouth is thelabium or lower lip. There is also an extra mouth part in some insects which is termed ashypopharynx which is usually located between themaxillac.[5]
Thoughinvertebratechordates – such as thetunicate larvae or thelancelets – 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.[6]
According to Hyman (1979), the evolution of the head in thevertebrates has occurred by the fusion of a fixed number of anterior segments, in the same manner as in other "heteronomously segmented animals". In some cases, segments or a portion of the segments disappear. The head segments also lose most of their systems, except for the nervous system. With the progressive development of cephalization, "the head incorporates more and more of the adjacent segments into its structure, so that in general it may be said that the higher the degree of cephalization the greater is the number of segments composing the head".[7]
In the 1980s, the "new head hypothesis" was proposed, suggesting that the vertebrate head is an evolutionary novelty resulting from the emergence ofneural crest and cranialplacodes.[8][9] In 2014, a transientlarva tissue of the lancelet was found to be virtually indistinguishable from the neural crest-derivedcartilage which forms the vertebrate skull, suggesting that persistence of this tissue and expansion into the entire headspace could be a viable evolutionary route to formation of the vertebrate head.[6]
The heads of humans and other animals are commonly recurringcharges inheraldry.[10] Heads of humans are sometimes blazoned simply as a "man's head", but are far more frequently described in greater detail, either characteristic of a particular race or nationality (such as Moors' heads, Saxons' heads, Egyptians' heads or Turks' heads), or specifically identified (such as the head of Moses in the crest of Hilton, or the head of St. John the Baptist in the crest of the London Company of Tallowchandlers).[10][11] Several varieties of women's heads also occur, including maidens' heads (often couped under the bust, with hair disheveled), ladies' heads, nuns' heads (often veiled), and occasionally queens' heads. The arms of Devaney of Norfolk include "three nun's heads veiled couped at the shoulders proper," and the bust of a queen occurs in the arms ofQueenborough, Kent.[10] Infants' or children's heads are often couped at the shoulders with a snake wrapped around the neck (e.g. "Argent, a boy's head proper, crined or, couped below the shoulders, vested gules, tarnished gold," in the arms of Boyman).[10]
One of the ways of drawingsketches of heads—asJack Hamm advises—is to develop it in six well-defined steps, starting with the shape of the head in the shape of an egg. The female head, in particular, is sketched in a double circle design procedure with proportions considered as an ideal of a female head. In the first circle, the division is made of five sections on thediameter, each section of five eyes width. It is then developed over a series of ten defined steps, with the smaller circle imposed partially over the larger circle at the lower end at the fourth stage. Eyes and chins are fitted in various shapes to form the head.[12]
Leonardo da Vinci, considered one of the world's greatest artists, drew sketches of human anatomy using grid structures. His image of the face drawn on the grid structure principle is in perfect proportion.[13] In this genre, using the technique of pen and ink, Leonardo created a sketch which is a "Study on the proportions of head and eyes" (pictured).
The head's function and appearance play an analogous role in the etymology of many technical terms.Cylinder head,pothead, andweatherhead are three such examples.
Cynocephaly – a characteristic of having the head of a dog or of a jackal. It is a widely attestedmythical phenomenon existing in many forms and contexts.
Khutang – a type ofharp often surmounted by a carven animal head, often a swan
Theriocephaly – in somereligious beliefs, the condition or quality of having the head of an animal, commonly used to refer the depiction in art of humans (ordeities) with animal heads
^abJandzik, 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.518 (7540):534–537.doi:10.1038/nature14000.PMID25487155.S2CID4449267.For lay summary see:"Evolution: How vertebrates got a head". Research.Nature (paper).516 (7530): 171. 11 December 2014.
.jpg)
.svg)
