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Meckel’s cartilage

Noun, pl. Meckel’s cartilages Also known as Meckelian’s cartilages. 1. The cartilaginous bar of the embryonic mandibular arch of which the distal end ossifies to form the malleus and most of the rest disappears in development, with the part adjacent to the malleus being replaced by fibrous membrane comprising the sphenomandibular ligament and the connective tissue covering most of the remaining part ossifying to form much of the mandible. ( 2. Hyaline cartilage formed in the mandibular process of the first branchial arch of vertebrate embryos. ( 3. The bilaterally paired, rod-like, cartilaginous ventral component of the lower jaw, or ventral mandibular arch. It is typically resorbed in adults. ( Syn: ventral mandibular cartilage Word origin: Named after Johann Friedrich Meckel (1781-1833), German...

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Meckel’s diverticulum

Noun 1. A true congenital diverticulum which is a slight bulge in the small intestine present at birth and a vestigial remnant of the omphalomesenteric duct (also called the vitelline duct or yolk stalk). It is the most common malformation of the gastrointestinal tract is present in approximately 2% of the population, with males more frequently experiencing symptoms. ( 2. The proximal part of the omphalomesenteric duct when persistent as a blind fibrous tube connected with the lower ileum. ( 3. A congenital diverticulum in the ileum resulting from incomplete closure of the yolk sac. ( 4. A pouch on the wall of the lower part of the intestine that is present at birth (congenital). The diverticulum may contain tissue that is the same as tissue of the stomach or pancreas. ( Word origin: From Latin deverticulum “a bypath,” from devertere “to turn...

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Medulla oblongata

/äˌblôNGˈgätə/ Noun 1. The lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla. The medulla contains the cardiac, respiratory, vomiting and vasomotor centers and deals with autonomic, involuntary functions, such as breathing, heart rate and blood pressure. ( 2. The lower portion of the brainstem. ( 3. The part of the vertebrate brain that is continuous posteriorly with the spinal cord and that contains the centers controlling involuntary vital functions. ( 4. Lower or hindmost part of the brain; continuous with spinal cord. ( 5. The continuation of the spinal cord within the skull, forming the lowest part of the brainstem and containing control centers for the heart and lungs. (Google Dictionary) Word origin: From Latin medulla, literally “marrow,” also “pith of plants,” of unknown origin, perhaps related to or influenced by medius...

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Meibomian gland

Noun, pl. Meibomaian glands 1. A special kind of sebaceous gland at the rim of the eyelids inside the tarsal plate, responsible for the supply of meibum, an oily substance that prevents evaporation of the eye’s tear film. Meibum prevents tear spillage onto the cheek, trapping tears between the oiled edge and the eyeball, and makes the closed lids airtight. ( 2. One of the long sebaceous glands of the eyelids that discharge a fatty secretion which lubricates the eyelids. ( Syn: tarsal gland Name origin: Named after Mei·bom, Heinrich (1638–1700), German physician. A professor of medicine at Helmstadt, Germany, Meibom accurately described the sebaceous glands of the eyelids in 1666. Although they are now identified with Meibom, the glands had been figured by the Italian anatomist Giulio Casserio (1561–1616) in 1609, and their existence has been known since the time of Galen....

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/mīˈōsəs/ Noun, pl. meioses (Genetics/Cytology) 1. Cell division that produces reproductive cells in sexually reproducing organisms; the nucleus divides into four nuclei each containing half the chromosome number (leading to gametes in animals and spores in plants). ( 2. A type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores. (Google Dictionary) 3. Cell division of a diploid cell into four haploid cells, which develop to produce gametes. ( 4. Cell division occurring in maturation of sex cells, wherein, over two successive cell divisions, each daughter nucleus receives half the number of chromosomes typical of the somatic cells of the species, so that the gametes are haploid. (Dorland’s Medical Dictionary for Health Consumers) 5. The special process of cell division in sexually reproducing organisms that results in the formation of gametes, consisting of two nuclear divisions in rapid succession that in turn result in the formation of four gametocytes, each containing half the number of chromosomes that is found in somatic cells. (The American Heritage® Medical Dictionary) (Rhetoric) 1. A figure of speech whereby something is made to seem smaller or less important than it actually is. ( Word origin: From Greek meiosis “a lessening,” from meioun “to lessen,” from meion...

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