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Mansa Musa was the ruler of the Mali Empire in West Africa. Details recorded here should be sourced; unknown information is left blank.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
The os opticus, also known as os nervi optici or Gemminger's ossicle,[1]: 595 is a bone found within the posterior sclera of the eye in many, but not all, species of birds. It is typically a ring- or horseshoe-shaped bone that encircles the optic nerve as it passes through the back of the eyeball. Its function is thought to be providing rigidity to the eye and supporting the optic nerve, which may be particularly important for birds that peck or require rapid visual accommodation. It was discovered by Max Gemminger in 1852.[2][3]
The bird eye is supported by a scleral ring at the front and a cartilaginous cup at the back. The os opticus is an ossification that forms in the cartilaginous cup, near where the optic nerve enters the eye.[4]
Its shape is variable among species. It is commonly horseshoe-shaped, but can range from a complete circle in some woodpeckers (e.g., the red-headed woodpecker, Melanerpes erythrocephalus), to a short arc in the domestic chicken (Gallus). In birds like toucans, doves, and woodpeckers, small additional bones known as "accessory ossifications" or "small bony particles" can be found near the main os opticus.[3]
Some birds possess other bones in the posterior sclera that form from the ossification of the scleral cartilage. These bones are only ever found in species that also have an os opticus. They are histologically similar to the os opticus, containing large marrow cavities filled with fat and blood cells. In birds studied during winter months, fat cells were observed to be predominant in these cavities. (Gemminger 1852) found such bones in the posterior sclera of 7 species of woodpeckers. In six of these species, these bones were not fused to the os opticus, while in one species they were.[3]
In the English sparrow, the bone has a cancellous marrow cavity containing fatty tissue and blood vessels. In females, medullary bone forms in it, similar to the marrow cavity of the femur. It forms during ovarian follicle growth, and is reabsorbed during shell formation.[3] See (Tiemeier 1953) for a description of its embryonic development in the English sparrow.
A 1950 study by Otto W. Tiemeier documented the os opticus in 219 species from 35 families of birds, including perching birds, woodpeckers, hummingbirds, toucans, kingfishers, and falcons.[4] It is notably absent in ratites like the ostrich and emu, as well as in loons and grebes. This distribution suggests the trait evolved after the divergence of these older lineages from the common ancestor of other birds.[3]
Even within species where it is present, its occurrence can be variable. In some species of Ardeidae (herons), Accipitridae (hawks and eagles), Phasianidae (pheasants and partridges), Columbidae (doves and pigeons), and Psittacidae (parrots), the bone is found in some individuals but is absent in others.[3]
A similar but likely non-homologous structure has been found in the fossil placoderm fish Dunkleosteus.[3]
The os opticus reinforces the posterior of the eyeball, making it more rigid. It is most highly developed in birds that obtain their food by pecking, such as woodpeckers, crows, and jays. The bone supports the optic nerve and may assist in rapid accommodation to near vision, an adaptation useful for these birds' feeding behaviors.[3]
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
The os opticus, also known as os nervi optici or Gemminger's ossicle, is a bone found within the posterior sclera of the eye in many, but not all, species of birds. It is typically a ring- or horseshoe-shaped bone that encircles the optic nerve as it passes through the back of the eyeball. Its function is thought to be providing rigidity to the eye and supporting the optic nerve, which may be particularly important for birds that peck or require rapid visual accommodation. It was discovered by Max Gemminger in 1852.
Max Gemminger (22 January 1820 – 18 April 1887) was a German physician, anatomist, zoologist and a curator at Royal Bavarian museum in Munich. He published a major catalogue of the beetles in the collections along with Baron Edgar von Harold, describing a number of taxa. He also worked on fish biology and collaborated with other zoologists of the period. Gemminger was born in Munich and went to a Latin school in Regensburg and from 1834 at Munich. He went to the Ludwig-Maximilians-Universität München where he received a doctorate in medicine. His 1847 dissertation was on the electric organs of the Mormyrus. He described four bones dorsal and ventral to the electric organ that were named later as "Gemminger bones" while a horseshoe shaped bone around the optic nerve of birds has been termed as "Gemminger ossicles" or os opticus. He then became the head of a municipal museum in Trieste. In 1849, he moved to the museum in Munich instigated by his former doctoral advisor, the embryologist Michael Pius Erdl (1815–1848) to work under the director Andreas Wagner. In 1864, he became an assistant to Carl Theodor von Siebold. From 1886, Gemminger worked on the beetle collections and produced a 12 volume catalog, Catalogus coleopterorum hucusque descriptorum synonymicus et systematicus, along with Baron Edgar von Harold over the course of 30 years. The work dealt with more than 77,000 species. He continued his studies on fish biology and was involved in the introduction of Lucioperca sandra to Lake Starnberg. Gemminger was a member of the Regensburg Zoological-Mineralogical Society, the "Lotos" society of Prague as well as the entomological society of Stettin.
Thomas Hobbes ( HOBZ; 5 April 1588 – 4 December 1679) was an English philosopher and political theorist, best known for his 1651 book Leviathan, in which he expounds an influential formulation of social contract theory. He is considered to be one of the founders of modern political philosophy. In his early life, overshadowed by his father's departure following a fight, he was taken under the care of his wealthy uncle. Hobbes's academic journey began in Westport, leading him to the University of Oxford, where he was exposed to classical literature and mathematics. He then graduated from the University of Cambridge in 1608. He became a tutor to the Cavendish family, which connected him to intellectual circles and initiated his extensive travels across Europe. These experiences, including meetings with figures like Galileo, shaped his intellectual development. After returning to England from France in 1637, Hobbes witnessed the destruction and brutality of the English Civil War from 1642 to 1651 between Parliamentarians and Royalists, which heavily influenced his advocacy for governance by an absolute sovereign in Leviathan, as the solution to human conflict and societal breakdown. Aside from social contract theory, Leviathan also popularised ideas such as the state of nature ("war of all against all") and laws of nature. His other major works include the trilogy De Cive (1642), De Corpore (1655), and De Homine (1658) as well as the posthumous work Behemoth (1681). Hobbes contributed to a diverse array of fields, including history, jurisprudence, geometry, optics, theology, classical translations, ethics, as well as philosophy in general, marking him as a polymath. Despite controversies and challenges to his reputation, including accusations of atheism and contentious debates with contemporaries, Hobbes's work profoundly influenced the understanding of political structure and human nature.
Lateral to either olfactory groove are the internal openings of the anterior and posterior ethmoidal foramina (or canals). The posterior ethmoidal foramen opens at the back part of this margin under cover of the projecting lamina of the sphenoid, and transmits the posterior ethmoidal vessels and nerve.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Mae Jemison, aboard Space Shuttle Endeavour in 1992.
