Which fontanelle is the largest

Synonyms: Large fontanelle Enlarged fontanelles Large fontanels Persistent wide fontanel Large fontanel Wide fontanelles. There are six membrane-covered openings between the cranial sutures in the incompletely ossified skull of the fetus or newborn infant that normally close sometime after birth anterior fontanel, cranial fontanel, mastoid fontanel, posterior fontanel, sphenoidal fontanel. All terms. Sutures allow the bones to move during the birth process. They act like an expansion joint. This allows the bone to enlarge evenly as the brain grows and the skull expands.

The result is a symmetrically shaped head. Some sutures extend to the forehead, while others extend to the sides and back of the skull. One suture in the middle of the skull extends from the front of the head to the back. The major sutures of the skull include the following:. Metopic suture. With respect to sutures, humans show a delayed pattern of ossification relative to other apes.

In humans the sutures remain patent and capable of growth until early adulthood late in the third decade of life , whereas in apes the sutures begin to fuse in childhood. Fusion of sutures in humans has been used as an age indicator, but fusion of the cranial sutures is highly variable and has been shown to be an unreliable indicator of age because of the range of variation in the timing of obliteration.

Also, the late fusion of the fontanelles and sutures permits a greater degree of postnatal growth of cerebral volume. Thus delayed fontanelle and suture closure is part of the human pattern of secondary altriciality.

One pathological condition of particular interest in terms of fontanelle closure and brain development is craniosynostosis. Craniosynostosis is a condition in which the sutures and fontanelles prematurely fuse and result in a change in the growth pattern of the skull.

In some cases this just results in a abnormally shaped head, while in other cases if brain development is disrupted there can be developmental impairments. It is a physical defect that might be caused by genetics or hormonal factors such as with exposure to high levels of thyroid hormone.

In humans with craniosynostosis, wormian bones extra sutural bones are significantly more frequent to develop with premature suture closure on the order of 3.

It has been documented that chimpanzees do have the occurrence of extra sutural bones. No cases of great ape craniosynostosis could be found in the literature but it is possible that if wormian bones are a response to craniosynostosis that chimpanzees do possess the necessary response for the pathology. Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event.

The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in as: the Last Common Ancestor LCA of humans and old world monkeys was 25, - 30, thousand 25 - 30 million years ago the Last Common Ancestor LCA of humans and chimpanzees was 6, - 8, thousand 6 - 8 million years ago the emergence of the genus Homo was 2, thousand 2 million years ago the Last Common Ancestor LCA of humans and neanderthals was thousand years ago the common ancestor of modern humans was - thousand years ago.

Most of the time, this sign will have been seen during the baby's first medical exam. Congenital anomalies of the central nervous system. In: Kliegman RM, St. Nelson Textbook of Pediatrics. Philadelphia, PA: Elsevier; chap Disorders of cranial volume and shape. Fenichel's Clinical Pediatric Neurology. Reviewed by: Neil K.

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