A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, 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, regardless of size.
Heads develop in animals by an evolutionary trend known as cephalization. In bilaterally symmetrical animals, nervous tissue concentrate at the anterior 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.
head
The human head is an anatomical unit that consists of the skull, hyoid bone and cervical vertebrae. The term "skull" collectively denotes the mandible (lower jaw bone) and the cranium (upper portion of the skull that houses the brain).[clarification needed ( The skull can also be described as being composed of the cranium, which encloses the cranial cavity, and the facial skeleton (includes the mandible). There are eight bones in the cranium and fourteen in the facial skeleton.[1])]
Sculptures of human heads are generally based on a skeletal structure that consists of a cranium, jawbone, and cheekbone. 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 of identism believe that the mind is identical to the brain. Philosopher John Searle asserts his identist beliefs, stating "the brain 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 of compound 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 the dorsal or located near or toward the head, two or three ocelli (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 of maxillae each of which is known as maxilliary palp. At the back side of the mouth is the labium or lower lip. There is also an extra mouth part in some insects which is termed as hypopharynx which is usually located between the maxillac.[5]
According to Hyman (1979), the evolution of the head in the vertebrates 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 of neural crest and cranial placodes.[8][9] In 2014, a transient larva 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 headspace could be a viable evolutionary route to formation of the vertebrate head.[6]
The heads of humans and other animals are commonly recurring charges in heraldry.[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 of Queenborough, 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]
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).
GRAPHENE 360 forms the structural base of the racquet, strategically positioned in the shaft and extending into the racquet head. It strengthens the frame, providing greater stability and optimized energy transfer from racquet to ball - maximizing the power of your game.
Transcript:\n\nMany parts of the body can be used as verbs in either a physical or a metaphorical sense. You can head a company, but if things go wrong you'll have to shoulder the blame, or face your investors. A good leader backs their employees, but if you don't toe the line you might get skinned. Did you muscle your way into that job? You might eye someone suspiciously, or wait for the police to finger a suspect. But if you need to get out of town, try thumbing a ride. You can ride with me if you can stomach the thought. I don't always sing along to the radio, but you might see me mouthing the words.","fb_legacy_url":null,"is_editor_choice":0,"is_archived":0,"is_published":1,"published_at":"2019-02-26 13:19:00","last_published_at":"2019-02-26 13:19:00","created_at":"2019-02-25 13:19:37","updated_at":"2022-05-17 16:03:21","tldr":null,"jw_id":"1QQElJRD"}; Dictionary Entries Near head he's
For vector/array based objects, head() (tail()) returnsa subset of the same dimensionality as x, usually ofthe same class. For historical reasons, by default they select thefirst (last) 6 indices in the first dimension ("rows") or along thelength of a non-dimensioned vector, and the full extent (all indices)in any remaining dimensions. head.matrix() andtail.matrix() are exported.
The default and array(/matrix) methods for head() andtail() are quite general. They will work as is for any classwhich has a dim() method, a length() method (onlyrequired if dim() returns NULL), and a [ method(that accepts the drop argument and can subset in alldimensions in the dimensioned case).
Head and neck cancers include cancers in the larynx, throat, lips, mouth, nose, and salivary glands. Tobacco use, heavy alcohol use, and infection with human papillomavirus (HPV) increase the risk of head and neck cancers. Explore the links on this page to learn more about the different types of head and neck cancer and how they are treated. We also have information about prevention, screening, research, clinical trials, and more.
A 200 response SHOULD include any header fields that indicate optional features implemented by the server and applicable to that resource (e.g., Allow), possibly including extensions not defined by this specification. The response body, if any, SHOULD also include information about the communication options. The format for such a
The Max-Forwards request-header field MAY be used to target a specific proxy in the request chain. When a proxy receives an OPTIONS request on an absoluteURI for which request forwarding is permitted, the proxy MUST check for a Max-Forwards field. If the Max-Forwards field-value is zero ("0"), the proxy MUST NOT forward the message; instead, the proxy SHOULD respond with its own communication options. If the Max-Forwards field-value is an integer greater than zero, the proxy MUST decrement the field-value when it forwards the request. If no Max-Forwards field is present in the request, then the forwarded request MUST NOT include a Max-Forwards field.
The semantics of the GET method change to a "conditional GET" if the request message includes an If-Modified-Since, If-Unmodified-Since, If-Match, If-None-Match, or If-Range header field. A conditional GET method requests that the entity be transferred only under the circumstances described by the conditional header field(s). The conditional GET method is intended to reduce unnecessary network usage by allowing cached entities to be refreshed without requiring multiple requests or transferring data already held by the client.
The semantics of the GET method change to a "partial GET" if the request message includes a Range header field. A partial GET requests that only part of the entity be transferred, as described in section 14.35. The partial GET method is intended to reduce unnecessary network usage by allowing partially-retrieved entities to be completed without transferring data already held by the client.
The HEAD method is identical to GET except that the server MUST NOT return a message-body in the response. The metainformation contained in the HTTP headers in response to a HEAD request SHOULD be identical to the information sent in response to a GET request. This method can be used for obtaining metainformation about the entity implied by the request without transferring the entity-body itself. This method is often used for testing hypertext links for validity, accessibility, and recent modification. 2ff7e9595c
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