Modern Greek refers to the dialects and varieties of the Greek language spoken in the modern era. Varieties of Modern Greek include several varieties, including Demotic, Pontic, Mariupolitan, Southern Italian, Demotic Greek comprises various regional varieties with minor linguistic differences, mainly in phonology and vocabulary. Due to the degree of mutual intelligibility of these varieties, Greek linguists refer to them as idioms of a wider Demotic dialect. Most English-speaking linguists however refer to them as dialects, emphasising degrees of variation only when necessary, Demotic Greek varieties are divided into two main groups and Southern. The main distinguishing feature common to Northern variants is a set of standard phonological shifts in unaccented vowel phonemes, becomes and and are dropped. The dropped vowels existence is implicit, and may affect surrounding phonemes, for example, Southern variants do not exhibit these phonological shifts. Examples of Northern dialects are Rumelian, Thessalian, Thracian, Demotic Greek has officially been taught in monotonic Greek script since 1982.
Polytonic script remains popular in intellectual circles, Katharevousa is a semi-artificial sociolect promoted in the 19th century at the foundation of the modern Greek state, as a compromise between Classical Greek and modern Demotic. It was the language of modern Greece until 1976. Katharevousa is written in polytonic Greek script, while Demotic Greek contains loanwords from Turkish, Italian and other languages, these have for the most part been purged from Katharevousa. It hails from Hellenistic and Medieval Koine and preserves characteristics of Ionic due to ancient colonizations of the region, Pontic evolved as a separate dialect from Demotic Greek as a result of the regions isolation from the Greek mainstream after the Fourth Crusade fragmented the Byzantine Empire into separate kingdoms. Rumeíka or Mariupolitan Greek is a dialect spoken in about 17 villages around the northern coast of the Sea of Azov in southern Ukraine, the Crimean Greek state continued to exist as the independent Greek Principality of Theodoro.
The Greek-speaking inhabitants of Crimea were invited by Catherine the Great to resettle in the new city of Mariupol after the Russo-Turkish War to escape the Muslim-dominated Crimea, mariupolitans main features have certain similarities with both Pontic and the northern varieties of the core dialects. Southern Italian or Italiot comprises both Calabrian and Griko varieties, spoken by around 15 villages in the regions of Calabria and Apulia, the Southern Italian dialect is the last living trace of Hellenic elements in Southern Italy that once formed Magna Graecia. Its origins can be traced to the Dorian Greek settlers who colonised the area from Sparta and Demotic are mutually intelligible to some extent, but the former shares some common characteristics with Tsakonian. Yevanic is an extinct language of Romaniote Jews. The language was already in decline for centuries until most of its speakers were killed in the Holocaust, the language was mostly kept by remaining Romaniote emigrants to Israel, where it was displaced by modern Hebrew.
Tsakonian evolved directly from Laconian and therefore descends from the Doric branch of the Greek language and it has limited input from Hellenistic Koine and is significantly different from and not mutually intelligible with other Greek varieties
Birds, a subgroup of Reptiles, are the last living examples of Dinosaurs. Birds live worldwide and range in size from the 5 cm bee hummingbird to the 2.75 m ostrich. They rank as the class of tetrapods with the most living species, at ten thousand. Birds are the closest living relatives of crocodilians, the fossil record indicates that birds evolved from feathered ancestors within the theropod group of saurischian dinosaurs. True birds first appeared during the Cretaceous period, around 100 million years ago, especially those in the southern continents, survived this event and migrated to other parts of the world while diversifying during periods of global cooling. Primitive bird-like dinosaurs that lie outside class Aves proper, in the broader group Avialae, have been found dating back to the mid-Jurassic period, around 170 million years ago. Birds have wings which are more or less developed depending on the species, the digestive and respiratory systems of birds are uniquely adapted for flight.
Some bird species of aquatic environments, particularly seabirds and some waterbirds, have evolved for swimming. Many species annually migrate great distances, Birds are social, communicating with visual signals and bird songs, and participating in such social behaviours as cooperative breeding and hunting and mobbing of predators. The vast majority of species are socially monogamous, usually for one breeding season at a time, sometimes for years. Other species have breeding systems that are polygynous or, Birds produce offspring by laying eggs which are fertilised through sexual reproduction. They are usually laid in a nest and incubated by the parents, most birds have an extended period of parental care after hatching. Some birds, such as hens, lay eggs even when not fertilised, songbirds and other species are popular as pets. Guano is harvested for use as a fertiliser, Birds prominently figure throughout human culture. About 120–130 species have become extinct due to human activity since the 17th century, human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them.
Recreational birdwatching is an important part of the ecotourism industry, the first classification of birds was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae. Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use, Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda, Aves and a sister group, the clade Crocodilia, contain the only living representatives of the reptile clade Archosauria
Modern humans are the only extant members of Hominina tribe, a branch of the tribe Hominini belonging to the family of great apes. Several of these hominins used fire, occupied much of Eurasia and they began to exhibit evidence of behavioral modernity around 50,000 years ago. In several waves of migration, anatomically modern humans ventured out of Africa, the spread of humans and their large and increasing population has had a profound impact on large areas of the environment and millions of native species worldwide. Humans are uniquely adept at utilizing systems of communication for self-expression and the exchange of ideas. Humans create complex structures composed of many cooperating and competing groups, from families. Social interactions between humans have established a wide variety of values, social norms, and rituals. These human societies subsequently expanded in size, establishing various forms of government, today the global human population is estimated by the United Nations to be near 7.5 billion.
In common usage, the word generally refers to the only extant species of the genus Homo—anatomically and behaviorally modern Homo sapiens. In scientific terms, the meanings of hominid and hominin have changed during the recent decades with advances in the discovery, there is a distinction between anatomically modern humans and Archaic Homo sapiens, the earliest fossil members of the species. The English adjective human is a Middle English loanword from Old French humain, ultimately from Latin hūmānus, the words use as a noun dates to the 16th century. The native English term man can refer to the species generally, the species binomial Homo sapiens was coined by Carl Linnaeus in his 18th century work Systema Naturae. The generic name Homo is a learned 18th century derivation from Latin homō man, the species-name sapiens means wise or sapient. Note that the Latin word homo refers to humans of either gender, the genus Homo evolved and diverged from other hominins in Africa, after the human clade split from the chimpanzee lineage of the hominids branch of the primates.
The closest living relatives of humans are chimpanzees and gorillas, with the sequencing of both the human and chimpanzee genome, current estimates of similarity between human and chimpanzee DNA sequences range between 95% and 99%. The gibbons and orangutans were the first groups to split from the leading to the humans. The splitting date between human and chimpanzee lineages is placed around 4–8 million years ago during the late Miocene epoch, during this split, chromosome 2 was formed from two other chromosomes, leaving humans with only 23 pairs of chromosomes, compared to 24 for the other apes. There is little evidence for the divergence of the gorilla, chimpanzee. Each of these species has been argued to be an ancestor of hominins
Andreas Vesalius was a 16th-century Flemish/Netherlandish anatomist and author of one of the most influential books on human anatomy, De humani corporis fabrica. Vesalius is often referred to as the founder of human anatomy. He was born in Brussels, which now part of Belgium, was part of the Habsburg Netherlands. He was professor at the University of Padua and became Imperial physician at the court of Emperor Charles V. Andreas Vesalius is the Latinized form of the Dutch Andries van Wesel and it was a common practice among European scholars in his time to Latinize their names. His name is given as Andrea Vesalius, André Vésale, Andrea Vesalio, Andreas Vesal, André Vesalio. Vesalius was born as Andries van Wesel to his father Anders van Wesel and mother Isabel Crabbe on 31 December 1514 in Brussels, which was part of the Habsburg Netherlands. His great grandfather, Jan van Wesel, probably born in Wesel, received a degree from the University of Pavia. There he studied the theories of Galen under the auspices of Jacques Dubois and it was during this time that he developed an interest in anatomy, and he was often found examining excavated bones in the charnel houses at the Cemetery of the Innocents.
Vesalius was forced to leave Paris in 1537 owing to the opening of hostilities between the Holy Roman Empire and France and returned to Leuven and he completed his studies there under Johann Winter von Andernach and graduated the following year. His thesis, Paraphrasis in nonum librum Rhazae medici arabis clariss, ad regem Almansorum de affectuum singularum corporis partium curatione, was a commentary on the ninth book of Rhazes. He remained at Leuven only a time before leaving after a dispute with his professor. After settling briefly in Venice in 1536, he moved to the University of Padua to study for his medical doctorate, on the day of his graduation he was immediately offered the chair of surgery and anatomy at Padua. He guest-lectured at the Bologna and the Pisa, prior to taking up his position in Padua, Vesalius traveled through Italy, and assisted the future Pope Paul IV and Ignatius of Loyola to heal those afflicted by Hansen’s disease. In Venice, he met the illustrator Johan van Calcar, a student of Titian and it was with van Calcar that Vesalius published his first anatomical text, Tabulae Anatomicae Sex, in 1538.
Previously these topics had been primarily from reading classical texts, mainly Galen. No attempt was made to confirm Galens claims, which were considered unassailable, Vesalius, in contrast, performed dissection as the primary teaching tool, handling the actual work himself and urging students to perform dissection themselves. Hands-on direct observation was, considered the only reliable resource, a break with medieval practice. Vesalius created detailed illustrations of anatomy for students in the form of six large woodcut posters, when he found that some of them were being widely copied, he published them all in 1538 under the title Tabulae anatomicae sex
Aelius Galenus or Claudius Galenus, often Anglicized as Galen and better known as Galen of Pergamon, was a prominent Greek physician and philosopher in the Roman Empire. The son of Aelius Nicon, an architect with scholarly interests, Galen received a comprehensive education that prepared him for a successful career as a physician. Galens understanding of anatomy and medicine was influenced by the then-current theory of humorism. His theories dominated and influenced Western medical science for more than 1,300 years, Medical students continued to study Galens writings until well into the 19th century. Galen saw himself as both a physician and a philosopher, as he wrote in his treatise entitled That the Best Physician is Also a Philosopher. Many of his works have been preserved and/or translated from the original Greek, although many were destroyed, although there is some debate over the date of his death, he was no younger than seventy when he died. In medieval Europe, Galens writings on anatomy became the mainstay of the medieval university curriculum.
Some of Galens ideas were incorrect, he did not dissect a human body, Galens original Greek texts gained renewed prominence during the early modern period. In the 1530s, Belgian anatomist and physician Andreas Vesalius took on a project to many of Galens Greek texts into Latin. Vesaliuss most famous work, De humani corporis fabrica, was influenced by Galenic writing. Galens name Γαληνός, Galēnos comes from the adjective γαληνός, Galen describes his early life in On the affections of the mind. Galen describes his father as an amiable, good. His studies took in each of the philosophical systems of the time. His father had planned a career for Galen in philosophy or politics and took care to expose him to literary. However, Galen states that in around AD145 his father had a dream in which the god Asclepius appeared and commanded Nicon to send his son to study medicine, there he came under the influence of men like Aeschrion of Pergamon and Satyrus. Asclepiea functioned as spas or sanitoria to which the sick would come to seek the ministrations of the priesthood, romans frequented the temple at Pergamon in search of medical relief from illness and disease.
It was the haunt of notable people such as Claudius Charax the historian, Aelius Aristides the orator, Polemo the sophist, in 148, when he was 19, his father died, leaving him independently wealthy. In 157, aged 28, he returned to Pergamon as physician to the gladiators of the High Priest of Asia, one of the most influential and wealthy men in Asia
Mammals are any vertebrates within the class Mammalia, a clade of endothermic amniotes distinguished from reptiles by the possession of a neocortex, three middle ear bones and mammary glands. All female mammals nurse their young with milk, secreted from the mammary glands, Mammals include the largest animals on the planet, the great whales. The basic body type is a quadruped, but some mammals are adapted for life at sea, in the air, in trees. The largest group of mammals, the placentals, have a placenta, Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale. With the exception of the five species of monotreme, all modern mammals give birth to live young, most mammals, including the six most species-rich orders, belong to the placental group. The largest orders are the rodents and Soricomorpha, the next three biggest orders, depending on the biological classification scheme used, are the Primates, the Cetartiodactyla, and the Carnivora. Living mammals are divided into the Yinotheria and Theriiformes There are around 5450 species of mammal, in some classifications, extant mammals are divided into two subclasses, the Prototheria, that is, the order Monotremata, and the Theria, or the infraclasses Metatheria and Eutheria.
The marsupials constitute the group of the Metatheria, and include all living metatherians as well as many extinct ones. Much of the changes reflect the advances of cladistic analysis and molecular genetics, findings from molecular genetics, for example, have prompted adopting new groups, such as the Afrotheria, and abandoning traditional groups, such as the Insectivora. The mammals represent the only living Synapsida, which together with the Sauropsida form the Amniota clade, the early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period, this group diverged from the line that led to todays reptiles. Some mammals are intelligent, with some possessing large brains, self-awareness, Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals and echolocation. Mammals can organize themselves into fission-fusion societies and hierarchies, most mammals are polygynous, but some can be monogamous or polyandrous.
They provided, and continue to provide, power for transport and agriculture, as well as commodities such as meat, dairy products, wool. Mammals are hunted or raced for sport, and are used as model organisms in science, Mammals have been depicted in art since Palaeolithic times, and appear in literature, film and religion. Defaunation of mammals is primarily driven by anthropogenic factors, such as poaching and habitat destruction, Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is accepted, McKenna & Bell and Wilson & Reader provide useful recent compendiums. Though field work gradually made Simpsons classification outdated, it remains the closest thing to a classification of mammals
Osteichthyes /ˌɒstiːˈɪkθi. iːz/, popularly referred to as the bony fish, is a diverse taxonomic group of fish that have skeletons primarily composed of bone tissue, as opposed to cartilage. The vast majority of fish are members of Osteichthyes, which is a diverse and abundant group consisting of 45 orders. It is the largest class of vertebrates in existence today, the group Osteichthyes is divided into the ray-finned fish and lobe-finned fish. The oldest known fossils of fish are about 420 million years ago. Osteichthyes can be compared to Euteleostomi, in paleontology, the terms are synonymous. However, recently published phylogenetic trees treat the Osteichthyes as a clade, bony fish are characterized by a relatively stable pattern of cranial bones, medial insertion of mandibular muscle in the lower jaw. The head and pectoral girdles are covered with large dermal bones, the eyeball is supported by a sclerotic ring of four small bones, but this characteristic has been lost or modified in many modern species.
The labyrinth in the ear contains large otoliths. The braincase, or neurocranium, is divided into anterior and posterior sections divided by a fissure. Early bony fish had simple lungs which helped them breathe in low-oxygen water, in many bony fish these have evolved into swim bladders, which help the body create a neutral balance between sinking and floating. They do not have fin spines, but instead support the fin with lepidotrichia and they have an operculum, which helps them breathe without having to swim. Bony fish have no placoid scales, most have smooth and overlapping ganoid, cycloid or ctenoid scales. Traditionally, Osteichthyes is considered a class, recognised on having a swim bladder, under this classification systems, the Osteichthyes are paraphyletic with regard to land vertebrates as the common ancestor of all Osteichthyes includes tetrapods amongst its descendants. The largest subclass, the Actinopterygii are monophyletic, but with the inclusion of the smaller sub-class Sarcopterygii and this has led to an alternative classification, splitting the Osteichthyes into two full classes.
Paradoxically, Sarcopterygii is under this scheme monophyletic, as it includes the tetrapods, most bony fish belong to the ray-finned fish. The phylogeny of living bony fishes is shown in the cladogram, for the majority this is their sole or main means of respiration. Lungfish and other species are capable of respiration through lungs or vascularized swim bladders. Other species can respire through their skin, and/or stomach, Osteichthyes are primitively ectothermic, meaning that their body temperature is dependent on that of the water
Wing of ilium
The wing of ilium is the large expanded portion which bounds the greater pelvis laterally. It presents for examination two surfaces—an external and an internal—a crest, and two anterior and a posterior. The external surface, known as the dorsum ossis ilium, is directed backward and lateralward behind, and downward and lateralward in front. It is smooth, convex in front, deeply concave behind, bounded above by the crest, below by the border of the acetabulum, in front. This surface is crossed in a direction by three lines—the posterior and inferior gluteal lines. The posterior gluteal line, the shortest of the three, begins at the crest, about 5 cm, the space between the anterior and posterior gluteal lines and the crest is concave, and gives origin to the Glutæus medius. Near the middle of this line a nutrient foramen is often seen. The inferior gluteal line, the least distinct of the three, begins in front at the notch on the border, curving backward and downward. The surface of bone included between the anterior and inferior gluteal lines is concave from above downward, convex from before backward, and gives origin to the Glutæus minimus.
Between the inferior gluteal line and the part of the acetabulum is a rough, shallow groove. The internal surface of the ala is bounded above by the crest, below, by the line, in front and behind. Behind the iliac fossa is a surface, divided into two portions, an anterior and a posterior. The anterior surface, so called from its resemblance in shape to the ear, is coated with cartilage in the fresh state, and articulates with a similar surface on the side of the sacrum. The posterior portion, known as the tuberosity, is elevated and rough, for the attachment of the posterior sacroiliac ligaments and for the origins of the Sacrospinalis. The crest of the ilium is convex in its general outline but is curved, being concave inward in front. It is thinner at the center than at the extremities, the surface of the crest is broad, and divided into external and internal lips, and an intermediate line. About 5 cm. behind the superior iliac spine there is a prominent tubercle on the outer lip. The anterior border of the ala is concave and it presents two projections, separated by a notch
Anatomical terminology is a form of scientific terminology used by anatomists and health professionals such as doctors. Anatomical terminology uses many terms and prefixes deriving from Ancient Greek. These terms can be confusing to those unfamiliar with them, but can be more precise reducing ambiguity, since these anatomical terms are not used in everyday conversation, their meanings are less likely to change, and less likely to be misinterpreted. By using precise anatomical terminology such ambiguity is eliminated, an international standard for anatomical terminology, Terminologia Anatomica has been created. Anatomical terminology has quite regular morphology, the prefixes and suffixes are used to add meanings to different roots. The root of a term refers to an organ, tissue. For example, in the disorder hypertension, the prefix hyper- means high or over, the roots and suffixes are often derived from Greek or Latin, and often quite dissimilar from their English-language variants. Latin names of such as musculus biceps brachii can be split up and refer to, musculus for muscle, biceps for two-headed.
The first word tells us what we are speaking about, the second describes it, when describing the position of anatomical structures, structures may be described according to the anatomical landmark they are near. These landmarks may include structures, such as the umbilicus or sternum, or anatomical lines, the cephalon or cephalic region refers to the head. This area is differentiated into the cranium, frons, auris, nausus, oris. The neck area is called the cervicis or cervical region, examples of structures named according to this include the frontalis muscle, submental lymph nodes, buccal membrane and orbicularis oculi muscle. Sometimes, unique terminology is used to reduce confusion in different parts of the body, for example, different terms are used when it comes to the skull in compliance with its embryonic origin and its tilted position compared to in other animals. Here, Rostral refers to proximity to the front of the nose, similarly, in the arms, different terminology is often used in the arms, in part to reduce ambiguity as what is the front, back and outer surfaces.
For this reason, the terms below are used, Radial referring to the radius bone, ulnar referring to the ulna bone, medially positioned when in the standard anatomical position. Other terms are used to describe the movement and actions of the hands and feet. International morphological terminology is used by the colleges of medicine and dentistry and it facilitates communication and exchanges between scientists from different countries of the world and it is used daily in the fields of research and medical care. The international morphological terminology refers to morphological sciences as a biological sciences branch, in this field, the form and structure are examined as well as the changes or developments in the organism
Internal obturator muscle
The internal obturator muscle, obturator internus muscle originates on the medial surface of the obturator membrane, the ischium near the membrane, and the rim of the pubis. It exits the pelvic cavity through the lesser sciatic foramen, the internal obturator is situated partly within the lesser pelvis, and partly at the back of the hip-joint. It functions to help laterally rotate femur with hip extension and abduct femur with hip flexion, the tendon inserts on the greater trochanter of the proximal femur. The internal obturator muscle is innervated by the nerve to internal obturator. This bony surface is covered by cartilage, which is separated from the tendon by a bursa. A bursa and elongated in form, is found between the tendon and the capsule of the hip-joint, it occasionally communicates with the bursa between the tendon and the ischium
Dinosaurs are a diverse group of reptiles of the clade Dinosauria that first appeared during the Triassic. Although the exact origin and timing of the evolution of dinosaurs is the subject of active research and they became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201 million years ago. Their dominance continued through the Jurassic and Cretaceous periods and ended when the Cretaceous–Paleogene extinction event led to the extinction of most dinosaur groups 66 million years ago, until the late 20th century, all groups of dinosaurs were believed to be extinct. As such, birds were the dinosaur lineage to survive the mass extinction event. This article deals primarily with non-avian dinosaurs, Dinosaurs are a varied group of animals from taxonomic and ecological standpoints. Birds, at over 10,000 living species, are the most diverse group of vertebrates besides perciform fish, using fossil evidence, paleontologists have identified over 500 distinct genera and more than 1,000 different species of non-avian dinosaurs.
Dinosaurs are represented on every continent by both extant species and fossil remains, while dinosaurs were ancestrally bipedal, many extinct groups included quadrupedal species, and some were able to shift between these stances. Elaborate display structures such as horns or crests are common to all dinosaur groups, evidence suggests that egg laying and nest building are additional traits shared by all dinosaurs.7 meters and heights of 18 meters and were the largest land animals of all time. Still, the idea that dinosaurs were uniformly gigantic is a misconception based in part on preservation bias, as large. Many dinosaurs were small, for example, was only about 50 cm long. Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the community believed dinosaurs to have been sluggish. Most research conducted since the 1970s, has indicated that all dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction.
The large sizes of some groups, as well as their seemingly monstrous and fantastic nature, have ensured dinosaurs regular appearance in best-selling books and films. Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, the term is derived from the Greek words δεινός and σαῦρος. Though the taxonomic name has often interpreted as a reference to dinosaurs teeth, claws. Instead, like many forms of reptile sub-groups, did not exhibit characteristics which were traditionally regarded as reptilian. Under phylogenetic nomenclature, dinosaurs are usually defined as the group consisting of Triceratops, their most recent common ancestor, Birds are now recognized as being the sole surviving lineage of theropod dinosaurs. In traditional taxonomy, birds were considered a class that had evolved from dinosaurs
Vertebrates /ˈvɜːrtᵻbrᵻts/ comprise all species of animals within the subphylum Vertebrata /-ɑː/. Vertebrates represent the majority of the phylum Chordata, with currently about 66,000 species described. Vertebrates include the fish and the jawed vertebrates, which include the cartilaginous fish. A bony fish known as the lobe-finned fishes is included with tetrapods, which are further divided into amphibians, mammals. Extant vertebrates range in size from the frog species Paedophryne amauensis, at as little as 7.7 mm, to the blue whale, vertebrates make up less than five percent of all described animal species, the rest are invertebrates, which lack vertebral columns. The vertebrates traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution, though their closest living relatives, hagfish do, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as Craniata when discussing morphology, molecular analysis since 1992 has suggested that hagfish are most closely related to lampreys, and so are vertebrates in a monophyletic sense.
Others consider them a group of vertebrates in the common taxon of craniata. The word origin of vertebrate derives from the Latin word vertebratus, the Proto-Indo-European language origins are still unclear. Vertebrate is derived from the vertebra, which refers to any of the bones or segments of the spinal column. All vertebrates are built along the basic body plan, a stiff rod running through the length of the animal, with a hollow tube of nervous tissue above it. In all vertebrates, the mouth is found at, or right below, the remaining part of the body continuing after the anus forms a tail with vertebrae and spinal cord, but no gut. However, a few vertebrates have secondarily lost this anatomy, retaining the notochord into adulthood, such as the sturgeon, jawed vertebrates are typified by paired appendages, but this trait is not required in order for an animal to be a vertebrate. All basal vertebrates breathe with gills, the gills are carried right behind the head, bordering the posterior margins of a series of openings from the pharynx to the exterior.
Each gill is supported by a cartilagenous or bony gill arch, the bony fish have three pairs of arches, cartilaginous fish have five to seven pairs, while the primitive jawless fish have seven. The vertebrate ancestor no doubt had more arches than this, as some of their relatives have more than 50 pairs of gills. In amphibians and some primitive fishes, the larvae bear external gills. These are reduced in adulthood, their function taken over by the gills proper in fishes, some amphibians retain the external larval gills in adulthood, the complex internal gill system as seen in fish apparently being irrevocably lost very early in the evolution of tetrapods