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Posterior Nasal Apertures
The choanae (singular choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the throat in tetrapods, including humans and other mammals (as well as crocodilians and most skinks). They are considered one of the most important synapomorphies of tetrapodomorphs, that allowed the passage from water to land. In animals with secondary palates, they allow breathing when the mouth is closed. Janvier, Philippe (2004) "Wandering nostrils". ''Nature'', 432 (7013): 23–24. In tetrapods without secondary palates their function relates primarily to olfaction (sense of smell). The choanae are separated in two by the vomer. Boundaries A choana is the opening between the nasal cavity and the nasopharynx. It is therefore not a structure but a space bounded as follows: * anteriorly and inferiorly by the horizontal plate of palatine bone, * superiorly and posteriorly by the sphenoid bone * laterally by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Horizontal Plate
The horizontal plate of palatine bone is a quadrilateral part of the palatine bone, and has two surfaces and four borders. Surfaces The superior surface, concave from side to side, forms the back part of the floor of the nasal cavity. The inferior surface, slightly concave and rough, forms, with the corresponding surface of the opposite bone, the posterior fourth of the hard palate. Near its posterior margin may be seen a more or less marked transverse ridge for the attachment of part of the aponeurosis of the tensor veli palatini. Borders The anterior border is serrated. It articulates with the palatine process of maxilla. The posterior border is concave, free, and serves for the attachment of the soft palate. Its medial end is sharp and pointed, and, when united with that of the opposite bone, forms a projecting process, the posterior nasal spine for the attachment of the musculus uvulae. The lateral border is united with the lower margin of the perpendicular plate, an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hagfish
Hagfish, of the class Myxini (also known as Hyperotreti) and order Myxiniformes , are eel-shaped, slime-producing marine fish (occasionally called slime eels). They are the only known living animals that have a skull but no vertebral column, although hagfish do have rudimentary vertebrae. Along with lampreys, hagfish are jawless; the two form the sister group to jawed vertebrates, and living hagfish remain similar to hagfish from around 300 million years ago. The classification of hagfish had been controversial. The issue was whether the hagfish was a degenerate type of vertebrate-fish that through evolution had lost its vertebrae (the original scheme) and was most closely related to lampreys, or whether hagfish represent a stage that precedes the evolution of the vertebral column (the alternative scheme) as is the case with lancelets. Recent DNA evidence has supported the original scheme. The original scheme groups hagfish and lampreys together as cyclostomes (or historica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diabolepis
''Diabolepis'' (or ''Diabolichthys'') is an extinct genus of very primitive lungfish which lived about 400 million years ago, in the Early Devonian period of South China. ''Diabolepis'' is the most basal known dipnoan. A rather small fish, the fossil has risen to prominence as it has four nares like most fish, while modern lungfish have only two, the hindmost pair having moved on to the palate serving as choanae. This proved that the internal nares of lungfish had evolved independently of those in tetrapods. This has made the internal nares a case of parallel evolution rather than a homology between lungfish and tetrapods. Characteristics ''Diabolepis'' has a prominent snout; the more recurvature the snout, the greater is the proportion of the premaxilla that is included within the mouth cavity. The teeth within the premaxilla are folded with polyplocodont structure. The maxilla was either toothless or absent or there may have been a gap between the premaxilla and the maxilla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parallel Evolution
Parallel evolution is the similar development of a trait in distinct species that are not closely related, but share a similar original trait in response to similar evolutionary pressure.Zhang, J. and Kumar, S. 1997Detection of convergent and parallel evolution at the amino acid sequence level. ''Mol. Biol. Evol.'' 14, 527-36. Parallel vs. convergent evolution Given a particular trait that occurs in each of two lineages descended from a specified ancestor, it is possible in theory to define parallel and convergent evolutionary trends strictly, and distinguish them clearly from one another. However the criteria for defining convergent as opposed to parallel evolution often are unclear in practice, so that arbitrary diagnosis is common in some cases. When two species are similar in a particular character, evolution is defined as parallel if the ancestors shared that similarity; if they did not, the evolution of that character in those species is defined as convergent. However, thi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kenichthys
''Kenichthys'' is a genus of sarcopterygian fish from the Devonian period, and a member of the clade tetrapodomorpha. The only known species of the genus is ''Kenichthys campbelli'' (named for the Australian palaeontologist Ken Campbell), the first remains of which were found in China in 1993.Chang, M. and Zhu, M. (1993) A new Middle Devonian osteolepidid from Qujing, Yunnan. ''Mem. Assoc. Australas. Palaeontol.'' 15 183-198 The genus is important to the study of the evolution of tetrapods due to the unique nature of its nostrils, which provide vital evidence regarding the evolutionary transition of fish-like nostrils to the tetrapod choanae.Zhu, M. and Ahlberg, P. (2004) The origin of the internal nostril of tetrapods. ''Nature'' 432 94-97 Description ''Kenichthys'' was a small tetrapodomorph, with a skull about long. While only areas of the front of the body are known, it seems likely that ''Kenichthys'' would have been similar in general body form to other basal sarcopter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of living fish species are ray-finned fish, belonging to the class Actinopterygii, with around 99% of those being teleosts. The earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period. Although they lacked a true spine, they possessed notochords which allowed them to be more agile than their invertebrate counterparts. Fish would continue to evolve through the Paleozoic era, diversifying into a wide variety of forms. Many fish of the Paleozoic developed external armor that protected them from predators. The first fish with jaws appeared in the Silurian period, after which many (such as sharks) became formidable marine predators rather than just the prey of arthropods. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetrapodomorphs
The Tetrapodomorpha (also known as Choanata) are a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advanced forms transitional between fish and the early labyrinthodonts, such as ''Tiktaalik'', have been referred to as "fishapods" by their discoverers, being half-fish, half-tetrapods, in appearance and limb morphology. The Tetrapodomorpha contains the crown group tetrapods (the last common ancestor of living tetrapods and all of its descendants) and several groups of early stem tetrapods, which includes several groups of related lobe-finned fishes, collectively known as the osteolepiforms. The Tetrapodamorpha minus the crown group Tetrapoda are the Stem Tetrapoda, a paraphyletic unit encompassing the fish to tetrapod transition. Among the characteristics defining tetrapodomorphs are modifications to the fins, notably a humerus with convex h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Funnel
A funnel is a tube or pipe that is wide at the top and narrow at the bottom, used for guiding liquid or powder into a small opening. Funnels are usually made of stainless steel, aluminium, glass, or plastic. The material used in its construction should be sturdy enough to withstand the weight of the substance being transferred, and it should not react with the substance. For this reason, stainless steel or glass are useful in transferring diesel, while plastic funnels are useful in the kitchen. Sometimes disposable paper funnels are used in cases where it would be difficult to adequately clean the funnel afterwards (for example, in adding motor oil into a car). Dropper funnels, also called dropping funnels or tap funnels, have a tap to allow the controlled release of a liquid. A flat funnel, made of polypropylene, utilises living hinges and flexible walls to fold flat. The term "funnel" may refer to the chimney or smokestack on a steam locomotive and commonly refers to the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Medial Pterygoid Plate
The pterygoid processes of the sphenoid (from Greek ''pteryx'', ''pterygos'', "wing"), one on either side, descend perpendicularly from the regions where the body and the greater wings of the sphenoid bone unite. Each process consists of a medial pterygoid plate and a lateral pterygoid plate, the latter of which serve as the origins of the medial and lateral pterygoid muscles. The medial pterygoid, along with the masseter allows the jaw to move in a vertical direction as it contracts and relaxes. The lateral pterygoid allows the jaw to move in a horizontal direction during mastication (chewing). Fracture of either plate are used in clinical medicine to distinguish the Le Fort fracture classification for high impact injuries to the sphenoid and maxillary bones. The superior portion of the pterygoid processes are fused anteriorly; a vertical groove, the pterygopalatine fossa, descends on the front of the line of fusion. The plates are separated below by an angular cleft, the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sphenoid Bone
The sphenoid bone is an unpaired bone of the neurocranium. It is situated in the middle of the skull towards the front, in front of the basilar part of the occipital bone. The sphenoid bone is one of the seven bones that articulate to form the orbit. Its shape somewhat resembles that of a butterfly or bat with its wings extended. Structure It is divided into the following parts: * a median portion, known as the body of sphenoid bone, containing the sella turcica, which houses the pituitary gland as well as the paired paranasal sinuses, the sphenoidal sinuses * two greater wings on the lateral side of the body and two lesser wings from the anterior side. * Pterygoid processes of the sphenoides, directed downwards from the junction of the body and the greater wings. Two sphenoidal conchae are situated at the anterior and inferior part of the body. Intrinsic ligaments of the sphenoid The more important of these are: * the pterygospinous, stretching between the spina angu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Palatine Bone
In anatomy, the palatine bones () are two irregular bones of the facial skeleton in many animal species, located above the uvula in the throat. Together with the maxillae, they comprise the hard palate. (''Palate'' is derived from the Latin ''palatum''.) Structure The palatine bones are situated at the back of the nasal cavity between the maxilla and the pterygoid process of the sphenoid bone. They contribute to the walls of three cavities: the floor and lateral walls of the nasal cavity, the roof of the mouth, and the floor of the orbits. They help to form the pterygopalatine and pterygoid fossae, and the inferior orbital fissures. Each palatine bone somewhat resembles the letter L, and consists of a horizontal plate, a perpendicular plate, and three projecting processes—the pyramidal process, which is directed backward and lateral from the junction of the two parts, and the orbital and sphenoidal processes, which surmount the vertical part, and are separated b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
