Lambda (anatomy)

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Lambda (anatomy)
Gray1193.svg
Side view of head, showing surface relations of bones. (Lambda labeled at center right.)
Details
Precursor Posterior fontanelle
Part of Skull, sagittal suture, lambdoid suture
System Skeletal
Identifiers
TA98 A02.1.00.017
TA2 419
FMA 264773
Anatomical terminology

The lambda is the meeting point of the sagittal suture and the lambdoid suture. This is also the point of the occipital angle. It is named after the Greek letter lambda.

Contents

Structure

The sagittal and lamboid sutures. Sagittal suture 2.jpg
The sagittal and lamboid sutures.

The lambda is the meeting point of the sagittal suture and the lambdoid suture. It may be the exact midpoint of the lambdoid suture, but often deviates slightly from the midline. [1] This is also the point of the occipital angle.

Development

In the foetus, the lambda is membranous, and is called the posterior fontanelle.[ citation needed ]

Etymology

The lambda is named after the Greek letter lambda, whose lowercase form (λ) resembles the junction formed by the sutures.

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<span class="mw-page-title-main">Skull</span> Bony structure that forms the head in vertebrates

The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone, however two parts are more prominent: the cranium and the mandible. In humans, these two parts are the neurocranium (braincase) and the viscerocranium that includes the mandible as its largest bone. The skull forms the anterior-most portion of the skeleton and is a product of cephalisation—housing the brain, and several sensory structures such as the eyes, ears, nose, and mouth. In humans, these sensory structures are part of the facial skeleton.

<span class="mw-page-title-main">Fontanelle</span> Anatomical feature of the infant human skull

A fontanelle is an anatomical feature of the infant human skull comprising soft membranous gaps (sutures) between the cranial bones that make up the calvaria of a fetus or an infant. Fontanelles allow for stretching and deformation of the neurocranium both during birth and later as the brain expands faster than the surrounding bone can grow. Premature complete ossification of the sutures is called craniosynostosis.

<span class="mw-page-title-main">Occipital bone</span> Bone of the neurocranium

The occipital bone is a cranial dermal bone and the main bone of the occiput. It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cerebrum. At the base of the skull in the occipital bone, there is a large oval opening called the foramen magnum, which allows the passage of the spinal cord.

<span class="mw-page-title-main">Parietal bone</span> Bone in the human skull which, when joined together, forms the sides and roof of the cranium

The parietal bones are two bones in the skull which, when joined at a fibrous joint, form the sides and roof of the neurocranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin paries (-ietis), wall.

<span class="mw-page-title-main">Craniosynostosis</span> Premature fusion of bones in the skull

Craniosynostosis is a condition in which one or more of the fibrous sutures in a young infant's skull prematurely fuses by turning into bone (ossification), thereby changing the growth pattern of the skull. Because the skull cannot expand perpendicular to the fused suture, it compensates by growing more in the direction parallel to the closed sutures. Sometimes the resulting growth pattern provides the necessary space for the growing brain, but results in an abnormal head shape and abnormal facial features. In cases in which the compensation does not effectively provide enough space for the growing brain, craniosynostosis results in increased intracranial pressure leading possibly to visual impairment, sleeping impairment, eating difficulties, or an impairment of mental development combined with a significant reduction in IQ.

<span class="mw-page-title-main">Sagittal suture</span> Midline joint between the parietal bones of the skull

The sagittal suture, also known as the interparietal suture and the sutura interparietalis, is a dense, fibrous connective tissue joint between the two parietal bones of the skull. The term is derived from the Latin word sagitta, meaning arrow.

<span class="mw-page-title-main">Lambdoid suture</span> Connective tissue between the parietal bones and the occipital bone of the skull

The lambdoid suture is a dense, fibrous connective tissue joint on the posterior aspect of the skull that connects the parietal bones with the occipital bone. It is continuous with the occipitomastoid suture.

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The asterion is a meeting point between three sutures between bones of the skull. It is an important surgical landmark.

<span class="mw-page-title-main">Occipitofrontalis muscle</span> Facial muscle helping to create facial expressions

The occipitofrontalis muscle is a muscle which covers parts of the skull. It consists of two parts or bellies: the occipital belly, near the occipital bone, and the frontal belly, near the frontal bone. It is supplied by the supraorbital artery, the supratrochlear artery, and the occipital artery. It is innervated by the facial nerve. In humans, the occipitofrontalis helps to create facial expressions.

<span class="mw-page-title-main">Confluence of sinuses</span> Venous sinus in the skull

The confluence of sinuses, torcular Herophili, or torcula is the connecting point of the superior sagittal sinus, straight sinus, and occipital sinus. It is below the internal occipital protuberance of the skull. It drains venous blood from the brain into the transverse sinuses. It may be affected by arteriovenous fistulas, a thrombus, major trauma, or surgical damage, and may be imaged with many radiology techniques.

<span class="mw-page-title-main">Superior sagittal sinus</span> Anatomical structure of the brain

The superior sagittal sinus, within the human head, is an unpaired area along the attached margin of the falx cerebri. It allows blood to drain from the lateral aspects of anterior cerebral hemispheres to the confluence of sinuses. Cerebrospinal fluid drains through arachnoid granulations into the superior sagittal sinus and is returned to venous circulation.

<span class="mw-page-title-main">Wormian bones</span>

Wormian bones, also known as intrasutural bones or sutural bones, are extra bone pieces that can occur within a suture (joint) in the skull. These are irregular isolated bones that can appear in addition to the usual centres of ossification of the skull and, although unusual, are not rare. They occur most frequently in the course of the lambdoid suture, which is more tortuous than other sutures. They are also occasionally seen within the sagittal and coronal sutures. A large Wormian bone at lambda is often called an Inca bone , due to the relatively high frequency of occurrence in Peruvian mummies. Another specific Wormian bone, the pterion ossicle, sometimes exists between the sphenoidal angle of the parietal bone and the great wing of the sphenoid bone. They tend to vary in size and can be found on either side of the skull. Usually, not more than several are found in a single individual, but more than one hundred have been once found in the skull of a hydrocephalic adult.

<span class="mw-page-title-main">Bregma</span> Meeting point of the coronal suture and the sagittal suture of the skull

The bregma is the anatomical point on the skull at which the coronal suture is intersected perpendicularly by the sagittal suture.

<span class="mw-page-title-main">Squamous part of occipital bone</span>

The squamous part of occipital bone is situated above and behind the foramen magnum, and is curved from above downward and from side to side.

<span class="mw-page-title-main">Posterior fontanelle</span>

The posterior fontanelle is a gap between bones in the human skull, triangular in form and situated at the junction of the sagittal suture and lambdoidal suture. It generally closes in 6–8 weeks from birth. The cranial point in adults corresponding the fontanelle is called lambda. A delay in closure is associated with congenital hypothyroidism.

<span class="mw-page-title-main">Fibrous joint</span> Fixed joints between bones held together by dense, fibrous tissue

In anatomy, fibrous joints are joints connected by fibrous tissue, consisting mainly of collagen. These are fixed joints where bones are united by a layer of white fibrous tissue of varying thickness. In the skull, the joints between the bones are called sutures. Such immovable joints are also referred to as synarthroses.

<span class="mw-page-title-main">Calvaria (skull)</span> Top part of the skull

The calvaria is the top part of the skull. It is the superior part of the neurocranium and covers the cranial cavity containing the brain. It forms the main component of the skull roof.

In arthropod and vertebrate anatomy, the vertex is the highest point of the head.

The fetal head, from an obstetrical viewpoint, and in particular its size, is important because an essential feature of labor is the adaptation between the fetal head and the maternal bony pelvis. Only a comparatively small part of the head at term is represented by the face. The rest of the head is composed of the firm skull, which is made up of two frontal, two parietal, and two temporal bones, along with the upper portion of the occipital bone and the wings of the sphenoid.

References

PD-icon.svgThis article incorporates text in the public domain from page 135 of the 20th edition of Gray's Anatomy (1918)

  1. Paxinos, George; Watson, Charles; Penisi, Michael; Topple, Ann (April 1985). "Bregma, lambda and the interaural midpoint in stereotaxic surgery with rats of different sex, strain and weight". Journal of Neuroscience Methods. 13 (2): 139–143. doi:10.1016/0165-0270(85)90026-3. ISSN   0165-0270. PMID   3889509. S2CID   36734348 via ScienceDirect.