The stapes is the third bone of the three ossicles in the middle ear. The stapes is a stirrup-shaped bone, and the smallest in the human body. It rests on the oval window, to which it is connected by an annular ligament. The stapes is described as having a base, resting on the oval window, as well as a head that articulates with the incus. These are connected by anterior and posterior limbs (). The stapes articulates with the incus through the incudostapedial joint. The stapes is the smallest bone in the human body, and measures roughly 3 x 2.5mm, greater along the head-base span.
Structure
Stapes
Stapes | Structure
Roughly 3 x 2.5mm Roughly 3 x 2.5mm. 3 x 2.5mm 3 x 2.5mm.
what are the 3 smallest bones in the human body
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Strapes is one of them
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The stapes is the third bone of the three ossicles in the middle ear. The stapes is a stirrup-shaped bone, and the smallest in the human body. It rests on the oval window, to which it is connected by an annular ligament. The stapes is described as having a base, resting on the oval window, as well as a head that articulates with the incus. These are connected by anterior and posterior limbs (). The stapes articulates with the incus through the incudostapedial joint. The stapes is the smallest bone in the human body, and measures roughly 3 x 2.5mm, greater along the head-base span.
Stapes | Structure
The stapes is one of three ossicles in mammals. In non-mammalian four-legged animals, the bone homologous to the stapes is usually called the columella; however, in reptiles, either term may be used. In fish, the homologous bone is called the "hyomandibular", and is part of the gill arch supporting either the spiracle or the jaw, depending on the species. The equivalent term in amphibians is the "".
Stapes | Animals
The stapes or stirrup is a bone in the middle ear of humans and other mammals which is involved in the conduction of sound vibrations to the inner ear. This stirrup-shaped bone is connected to the oval window by its annular ligament, which allows the footplate to transmit sound energy through the oval window into the inner ear. The stapes is the smallest and lightest bone in the human body, and is so-called because of its resemblance to a stirrup ().
Stapes | Introduction
The stapes is commonly described as having been discovered by the professor Giovanni Filippo Ingrassia in 1546 at the University of Naples, although this remains the nature of some controversy, as Ingrassia's description was published posthumously in his 1603 anatomical commentary '. Spanish anatomist Pedro Jimeno is first to have been credited with a published description, in ' (1549). The bone is so-named because of its resemblance to a stirrup (), an example of a late Latin word, probably created in mediaeval times from "to stand" (), as stirrups did not exist in the early Latin-speaking world.
Stapes | History
The largest bone in the body is the femur or thigh-bone, and the smallest is the stapes in the middle ear.
Bone | Introduction
The stapedius is the smallest skeletal muscle in the human body. At just over one millimeter in length, its purpose is to stabilize the smallest bone in the body, the stapes.
Stapedius muscle | Introduction
For example, the lower branch of the squamosal bone is shortened to offset the tall dorsal process of quadratojugal which connects to it. On the other hand, the rear branch jugal bone lengthens to fill some of the space left by the shortening of the anterior process of the quadratojugal. In archosauriforms, the jugal even re-encloses the lower temporal fenestra. The stapes are long, thin, and solid, without a perforating hole (stapedial foramen) present in the more robust stapes of other reptiles.
Archosauromorpha | Skull
A much more detailed description of the first two ossicles followed in Andreas Vesalius' "De humani corporis fabrica" in which he devoted a chapter to them. Vesalius was the first to compare the second element of the ossicles to an anvil although he offered the molar as an alternative comparison for its shape. The first published description of the stapes came in Pedro Jimeno's "Dialogus de re medica" (1549) although it had been previously described in public lectures by Giovanni Filippo Ingrassia at the University of Naples as early as 1546. The term "ossicle" derives from , a diminutive of "bone" (; genitive ).
Ossicles | History
The stapes develops from the second pharyngeal arch during the sixth to eighth week of embryological life. The central cavity of the stapes, the obturator foramen, is due to the presence embryologically of the stapedial artery, which usually regresses in humans during normal development.
Stapes | Development
Surgery may be complicated by a persistent stapedial artery, fibrosis-related damage to the base of the bone, or obliterative otosclerosis, resulting in obliteration of the base.
Stapes | Clinical relevance
The bony palate is short, with its posterior end often located between the third molars. The alisphenoid strut, an extension of the alisphenoid bone of the skull that separates two foramina (openings) in the skull, is present in some individuals. The mastoid bone usually contains some openings. In the holotype, the head and body length is 130 mm, the tail length is 160 mm, the hindfoot length (without claws) is 31 mm, the ear length is 27 mm, and the skull length is 35.7 mm.
Nephelomys levipes | Introduction
These are the most unusual of the braincase bones, and were previously misidentified as stapes. While they are not stapes, it is difficult to be certain what they are. As mentioned, they are sutured to the tubera basioccipitalia, and so could not have moved freely, meaning that they were not bones for the transmission of sound in this manner. Medially, they are sutured to the posterodorsal margins of the tubera basioccipitalia by a strongly serrate and partially intergrown suture. The posterior surface of this forms a steeply inclined trough running from the suture to the distal extremity of the paraoccipital process.
Phantomosaurus | Opisthotic bones
The bone flap represents the first and second epiparietal pairs, the "P1s" and "P2s", as is evidenced by the osteoderm points still being visible, those of the first pair pointing to the front near the midline, those of the second pair forming the corners of the flap. The third epiparietals, pointing to behind, together form a pincer-like construction around the notch. At each rear corner of the frill a very large osteoderm is present. As it spans the suture between the squamosal and the parietal, this has been called an epiparietosquamosal or "EPS".
Spiclypeus | Skeleton
The morphology of the stapes suggests that the animal was capable of hearing high-frequency sound. "B. woodi" does not possess lateral line sulci or an ossified branchial system. The principal method of respiration was probably buccal (gulping air through mouth) rather than costal (expanding chest volume to take in air), indicated by the small straight ribs.
Balanerpeton | Introduction
The stapedius emerges from a pinpoint foramen in the apex of the pyramidal eminence (a hollow, cone-shaped prominence in the posterior wall of the tympanic cavity), and inserts into the neck of the stapes.
Stapedius muscle | Structure
The hindwing of an average adult is generally 30 mm or larger.
Tonyosynthemis claviculata | Body
The skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs, heart and spinal cord. Although the teeth do not consist of tissue commonly found in bones, the teeth are usually considered as members of the skeletal system. The biggest bone in the body is the femur in the upper leg, and the smallest is the stapes bone in the middle ear. In an adult, the skeleton comprises around 14% of the total body weight, and half of this weight is water.
Skeleton | Humans
The configuration of the stapes is intermediate between non-amniote tetrapods and amniotes. On the one hand, its connection to the otic notch is unusual, since true reptiles and other amniotes have lost an otic notch, forcing the tympanum and stapes to shift downwards towards the quadrate bone of the jaw joint. On the other hand, the thin, sensitive structure of "Seymouria"'s stapes is a specialization over most non-amniote tetrapods, which have a thick stapes useless for hearing yet useful for reinforcing the skull. The inner ear of "Seymouria baylorensis" retains a cochlear recess located behind (rather than below) the vestibule, and its anterior semicircular canal was likely encompassed by a cartilaginous (rather than bony) supraoccipital.
Seymouria | Skull
Writing in the journal La Nature, de Lapouge describes the bones in detail: "I think it unnecessary to note that these bones are undeniably human, despite their enormous size... The first is the middle part of the shaft of a femur, 14 cm length, almost cylindrical in shape, and the circumference of the bone is 16 cm... The second piece is the middle and upper part of the shaft of a tibia... The circumference is 13 cm at the nutrient foramen... the length of fragment is 26 cm... The third, very singular, was regarded by good anatomists as the lower part of a humerus...
Giant of Castelnau | Discovery
The bone has a length of seven centimetres. This manual element shows a prominent dorsomedial process, a feature shared with the much smaller "Ornitholestes" which occasioned the specific name. The process with "Ornitholestes" is much less distinctive though. On its upper end there is only one cotyle, from which von Huene deduced it must have been a metacarpal. However, several coelurosaurian groups lack a second cotyle on the first phalanx also. If "Rapator" had a build like "Australovenator", it would have attained a considerable size: a body length of nine metres (30 ft) has been estimated.
Rapator | Description
Sexual dimorphism is the difference of size in male and female skeletons. The two bone structures that are used to determine whether a person is male or female are the skull and pelvis. The bones can also be used to reveal the age of the person before they died. At birth the human cranial vault consists of seven separate bones; by age 5 these bones have knitted together at the cranial sutures. At about the age of 30 , the sutures generally begin to fill in with bone and smooth out. Another way to tell the age of bones is by bone osteons under a microscope or look for arthritis indicators on the bones.
Osteology | Introduction
The scapes are short, measuring , and the pedicel (the second segment of the antenna) is The flagellomeres vary in length, ranging between . The clypeus is shallow and measures (when excluding the denticles). It is broad, and the distance between its lateral-most denticles is . It is also more concave-shaped than it is straight. The oral margin of the clypeus is lined with a row of 30 denticles, which are peg-shaped. They also have rounded apices. The row of clypeal margin denticles is composed of two short rows. Each row is composed of 15 denticles each. The mandibles are short and barely overlap medially.
Zigrasimecia | "Z. tonsora"
The stapes, the bone transmitting sound waves from the eardrum to the middle ear, is elongated and not pierced by a foramen. Pterygoid teeth are typically lacking.
Ichthyosaur | Skull
Situated between the incus and the inner ear, the stapes transmits sound vibrations from the incus to the oval window, a membrane-covered opening to the inner ear. The stapes is also stabilized by the stapedius muscle, which is innervated by the facial nerve.
Stapes | Function
The cage is circular and is approximately 4.5 meters in diameter and 5 meters in height. Two pieces of bone, that have been emptied of marrow, are stuck in the side of it. Several tapestries are hung on it.
Spider (Bourgeois) | The cage
Similarly, the sacrum is usually counted as a single bone, rather than five fused vertebrae. There is also a variable number of small sesamoid bones, commonly found in tendons. The patella or kneecap on each side is an example of a larger sesamoid bone. The patellae are counted in the total, as they are constant. The number of bones varies between individuals and with age – newborn babies have over 270 bones some of which fuse together. These bones are organized into a longitudinal axis, the axial skeleton, to which the appendicular skeleton is attached.
Skeleton | Humans
The length of the holotype individual was in 2019 estimated at long. Such a body size is rather limited for a troodontid. The specimen may represent an adult or subadult individual, due to the lack of cranial and body proportions associated with juvenile individuals. Nevertheless, either assignation would not be much different; for instance, the estimated would become . The describing authors established some derived or apomorphic traits relative to the Paraves. The jugal bone is pneumatised. The rear branch of the lacrimal bone is short, with less than 15% of the length of the descending branch, measured from the inner corner downwards.
Hesperornithoides | Description
The part of the skeleton that is ‘tucked under’ (the doublure) has no sutures crossing it to form a rostral plate.The thorax has 11 (rarely 10) segments, the side lobes (or pleurae) are furrowed, and the articulating facets distinct.
Phacopina | Description
The clypeus is setose, meaning that it bears bristles or setae, except on the middle part. The mandibles are small and only contain two teeth. The antennae are moderately long, the scapes are very short but the pedicel is even shorter. The mesosoma measures and is setose. Several setae are seen around the metanotum (the dorsal sclerite) and propodeum. The coxae, the proximal segment and functional base of the leg, are setose (bearing bristle or setae), inflated and large. The metapleural gland opening is small and noticeable, located away from the propodeum and above the metacoxa (the hind of the coxa).
Sphecomyrma | "S. mesaki"
The resulting three-boned structure is still seen in modern monotremes, but in all other living mammals, the procoracoid has disappeared, and the coracoid bone has fused with the scapula, to become the coracoid process. These changes are associated with the upright gait of mammals, compared with the more sprawling limb arrangement of reptiles and amphibians; the muscles formerly attached to the procoracoid are no longer required. The altered musculature is also responsible for the alteration in the shape of the rest of the scapula; the forward margin of the original bone became the spine and acromion, from which the main shelf of the shoulder blade arises as a new structure.
Scapula | In other animals
Scapes up to 15 cm tall bearing 4-10 bell-shaped magenta flowers.
Allium narcissiflorum | Introduction
The tympanic bullae are small and less than in length. The width of the basioccipital is less than . The width of the infraorbital canals is very narrow being less than . The width across the nasals is very narrow and their length is less than . They have medium-sized auditory bullae with a length of less than . The shield bullae have a shallow depth of less than . The skull also has a narrow basioccipital and is very broad across the carotid foramina. The mouth consists of a mandible whose height is less than with a mandible ramus depth of less than .
Omilteme cottontail | Anatomy
It is occupied by the base of the stapes, the circumference of which is fixed by the annular ligament to the margin of the foramen.
Oval window | Introduction
This species is likely now extinct.
Theliderma stapes | Conservation
herschelensis". Assuming that only a few vertebrae are missing from the skeleton, the animal is estimated to be about 2.5 to 3 metres in length. The snout is long and thin, with numerous tooth sockets. However, very few of the thin, sharp teeth remain.
Ancient Echoes Interpretive Centre | "Dolichorhynchops herschelensis"
A sacral length of around 6.5 is deduced. Dames observed 20 caudal vertebrae; Wellnhofer posits 21. Dames also noted the similarity in the long, rod-like structures of the tail to those in the flying pterosaur "Rhamphorhynchus", considering them to be ossified tendons. Thin, pointed cervical ribs begin at the third vertebra. The longest are about 50 mm and total eleven in number. Gastralia, or belly ribs, are arranged in 10 parallel rows and their position is suggested as evidence of post-mortem shrinking of the body. The scapulae are separated by about 17 mm and are flattened, narrow, and positioned much in their natural position.
Specimens of Archaeopteryx | Trunk
Such structures include a shelf at the rear of the surangular and a thick articular bone which has a tall retroarticular process with an inner prong pierced by a "chorda tympani" foramen.
Prestosuchus | Skull
Fused bones include those of the pelvis and the cranium. Not all bones are interconnected directly: There are three bones in each middle ear called the ossicles that articulate only with each other. The hyoid bone, which is located in the neck and serves as the point of attachment for the tongue, does not articulate with any other bones in the body, being supported by muscles and ligaments. There are 206 bones in the adult human skeleton, although this number depends on whether the pelvic bones (the hip bones on each side) are counted as one or three bones on each side (ilium, ischium, and pubis), whether the coccyx or tail bone is counted as one or four separate bones, and does not count the variable wormian bones between skull sutures.
Skeleton | Humans
Close to the wrist, the ulna has a styloid process.
Ulna | Structure
The shape and form of the ligament have been found in humans cadavers to vary from a rounded cord to a flat membrane. Further, it is not found in all humans being variably found to be absent in half of arms, and a third or 15% of people. It is found in most primates though not in the family of New World monkeys that includes spider and woolly monkeys called atelines.
Oblique cord | Variation
Scattered hairs cover the body. Just in front of the anus there is in Chaetosorna a double, and in Tristicochaeta a triple row of about fifteen stout cylindrical projections upon which the animals creep. The females are a little larger than the males; in Ch. claparedii the former attain a length of 1.5 mm., the latter of 1.12 mm. The mouth opens into an oesophagus which passes into an intestine; this opens by a ventral anus situated a little in front of the posterior end. The testis is single, and its duct opens with the anus, and is provided with a couple of spicules.
Chaetosomatida | Introduction
Furculae have only rarely been recovered from early theropod fossils; other examples include those of "Segisaurus" and "Coelophysis". The lower arm bones, the ulna and the radius, had a length of about seven centimetres. Hand elements are present but a formula of the phalanges could not determined. In the pelvis, the pubic bone had a length of 212 millimetres. It points obliquely to the front. The pubic foot is moderately broadened in side view, bot at the front and at the rear. The shaft of the ischium is with a length of 129 millimetres markedly shorter than the pubic shaft.
Dracoraptor | Skeleton
"Pneumatoraptor" differs from other theropods in having a narrow shoulder blade that is nearly circular in cross section, as well as having a large opening in the bone to house a hollow air sac cavity. The bone is small, indicating that the animal was only about half the size of the related "Sinornithosaurus" or 0.73 m (2.2 ft). The shoulder girdle is L-shaped, showing it to be a member of the group Paraves, which also includes the dromaeosaurids, troodontids, and birds. While the "Pneumatoraptor" remains are too incomplete to tell which, if any, of these specific groups it belongs to, many of the bones features are similar to dromaeosaurids.
Pneumatoraptor | Description
Occasionally the joints between the ossicles become rigid. One condition, otosclerosis, results in the fusing of the stapes to the oval window. This reduces hearing and may be treated surgically.
Ossicles | Clinical relevance
In monotremes, the coracoid is a separate bone. Reptiles, birds, and frogs (but not salamanders) also possess a bone by this name, but is not homologous with the coracoid process of mammals. Analyses of the size and shape of the coracoid process in "Australopithecus africanus" (STS 7) have shown that in this species it displayed a prominent dorsolateral tubercle placed more laterally than in modern humans. This reflect, according to one interpretation, a scapula positioned high on a funnel-shaped thorax and a clavicle positioned obliquely as in extant great apes.
Coracoid process | Other animals
In such animals, the scapula is usually a relatively simple plate, lacking the projections and spine that it possesses in mammals. However, the detailed structure of these bones varies considerably in living groups. For example, in frogs, the procoracoid bones may be braced together at the animal's underside to absorb the shock of landing, while in turtles, the combined structure forms a Y-shape in order to allow the scapula to retain a connection to the clavicle (which is part of the shell). In birds, the procoracoids help to brace the wing against the top of the sternum. In the fossil therapsids, a third bone, the true coracoid, formed just behind the procoracoid.
Scapula | In other animals
The wrist includes six bones. The hand paddle has five digits; the phalangeal formula is uncertain, but the count for one large individual, from "thumb" to fifth "finger", is 4-8-9-8-6. The pelvis includes equant pubic bones, ischia, and blade-shaped ilia connecting the pelvis to the vertebral column. The acetabulum is formed by surfaces on the pubic bones and ischia. Similar to the pectoral girdle, there is a pair of holes between the ischia and pubic bones. The hindlimbs are long and narrow, and in adults, they are much smaller than the forelimbs. The thigh bones are straight. The lower hindlimb includes two roughly equal-sized bones, the robust tibia and the semilunate-shaped fibula.
Plesiosaurus | Limbs
Nudibranchs vary in adult size from .
Nudibranch | Anatomical description
The holotype specimen consists of the remains of a small individual. Because most of the vertebral column is absent, its body length cannot be directly determined, but a comparison can be made with the previously smallest known ornithomimosaur, the 1.6 metres long "Shenzhousaurus", which has a thighbone length of 191 millimetres, while the femur length of "Hexing" is 135 millimetres. Such a small body size was among ornithomimosaurs up till now only known from juveniles but the holotype is not a young animal as is shown by the complete fusion of the skull bones, the neck ribs, the scapulocoracoid and the ankle bones.
Hexing | Description
Caudal to what will eventually become the stapes, Reichert's cartilage also forms the styloid process of the temporal bone. The cartilage between the hyoid bone and styloid process will not remain as development continues, but its perichondrium will eventually form the stylohyoid ligament.
Pharyngeal arch | Reichert's cartilage
Males have a body about 13 mm long, females about 19 mm long.
Zorodictyna oswaldi | Introduction
They strongly project to the side, at an angle of 50° with the midline of the skull. Their points gradually curve to below. The relatively flat skull frill has a triangular profile in top view, with slightly convex sides and diverging rear corners separated by a broad notch on the rear edge. The structure is pierced by large elongated openings, the parietal fenestrae. The frill of "Spiclypeus" features a unique pattern of skin ossifications or osteoderms ornamenting its edge. The side bones of the neck shield, the squamosals, bear episquamosals, with the holotype individual six on the left side and seven on the right side.
Spiclypeus | Skeleton
The long bone category includes the femora, tibiae, and fibulae of the legs; the humeri, radii, and ulnae of the arms; metacarpals and metatarsals of the hands and feet, the phalanges of the fingers and toes, and the clavicles or collar bones. The long bones of the human leg comprise nearly half of adult height. The other primary skeletal component of height are the vertebrae and skull. The outside of the bone consists of a layer of connective tissue called the periosteum. Additionally, the outer shell of the long bone is compact bone, then a deeper layer of cancellous bone (spongy bone) which contains in the medullary cavity the bone marrow.
Long bone | Introduction
The filaments are preserved with a gap between the bones, which several authors have noted corresponds closely to the expected amount of skin and muscle tissue that would have been present in life. The feathers are closest to the bone on the skull and end of the tail, where little to no muscle was present, and the gap increases over the back vertebrae, where more musculature would be expected, indicating that the filaments were external to the skin and do not correspond with subcutaneous structures. The filaments exhibit random orientations and are often wavy, which has been interpreted as evidence that they were soft and pliable in life.
Sinosauropteryx | Feathers
It is entirely clad in 100,000 square metres of inflated ETFE foil cushions arranged as an apparently random cellular structure.
Membrane structure | Introduction
This full-page image is a frontal view of a human skeleton, with labels describing the major bones of the body.
Grete Herball | Anatomical chart
Clamp connections are present in the hyphae of all tissues.
Leucopholiota decorosa | Description
"C. microcephala" is known from a single fossil, a winged gyne preserved in profile view. The body has an approximate length of with an essentially square head. The head is 1.5 times shorter than the mesosoma and has a sculpturing of small pits. The clypeus has a trapazohedral shape to the lower edge, and the eyes are placed at the middle point of the head. The antennae have segments that are 2 times as long as they are wide, with a scape which reaches to the back edge of the head. The mandibles are small, being under half the head length and each chewing side is toothed.
Cyrtopone | "C. microcephala"
The reason for this evolutionary change is still unknown; however, it may be to assist in grasping small objects and thin branches.
Sesamoid bone | Other animals
On the proboscis, there are approximately 20 very fine hooks found on each of 40 rows. The two lemnisci are longer than the body length and are folded in the body cavity. Females are 2.13 mm long by 0.83 mm in maximum width and the proboscis is 0.36 mm long by 0.44 mm in maximum width. The male is smaller being 1.43 mm long by 0.53 mm in maximum width and the proboscis is 0.44 mm long by 0.74 mm in maximum width.
Apororhynchus | Species
In some of the eyeless genera ("Ductina") the suture coincides with the marginal suture, and thus appears to be absent. The part of the skeleton that is "tucked under" (the doublure) has no sutures crossing it to form a rostral plate. The thorax has 11 (rarely 10) segments, the side lobes (or pleurae) are furrowed, and the articulating facets distinct. The tailshield (or pygidium) is always smaller than the headshield (or cephalon), a situation called micropygous. In the Phacopidae a merger of the anterior and the two pairs of neighbouring lobes of the glabella forms a frontal lobe that expands forward and can be inflated and overhanging the frontal border.
Phacopidae | Description
Overall, the skeletal anatomy of this genus is well documented, and restorations have been published in several papers, including skeletal restorations and models. The skeleton is known well enough that a detailed reconstruction of the hip and hindlimb muscles has been made. The animal's size has been estimated in the 2.5–4.0 m range for length (8.2–13.1 ft) for various specimens, and a weight of 200–300 kilograms (450–660 pounds), with the large type specimen of "T. garbanii" estimated at 4–4.5 meters (13.1–14.8 feet) long. As discussed more fully under "Discovery, history, and species", it may have been sexually dimorphic, with one sex larger than the other.
Thescelosaurus | Description
An enormous chandelier of bones, which contains at least one of every bone in the human body, hangs from the center of the nave with garlands of skulls draping the vault. Other works include piers and monstrances flanking the altar, a coat of arms of the House of Schwarzenberg, and the signature of František Rint, also executed in bone, on the wall near the entrance.
Sedlec Ossuary | Introduction
The gyne is notably larger than the worker, at approximately long, and has a head that is wider than long when the mandibles are excluded. Also unlike the worker, the eyes are placed at the midpoint of the head, though they are small as the workers are. There are a number of denticles along the chewing margin on the large triangle shaped mandibles. While the scape extends beyond the back of the head, its total length is less than that of the head.
Paraneuretus | "P. dubovikoffi"
The ossicles are suspended in the head and loosely coupled to the skull. When the head moves, the ossicles move out of phase with the head, but still follow the same cyclic motion. This causes the stapes to move in and out of the oval window. When vibrations come from the mastoid, inertial bone-conduction is greatest below 800 Hz. Putting the bone vibrator on the forehead instead of the mastoid does not significantly create this affect.
Bone conduction auditory brainstem response | Inertial bone-conduction
"K. cadburyi" is distinguished by the authors from all extant monotremes, as well as from fossil tachyglossids, by the presence of a broad, marginated, shallow bicipital sulcus on the proximal humerus, which extends distally onto the waist of the bone. It is also distinguished by the presence of a trochlear-form ulnar articulation and a distal olecranon fossa. Pridmore "et al" find these features sufficient to distinguish it from "Steropodon" as well as other non-tachyglossid but similar monotremes such as "Obdurodon", "Kollikodon", "Teinolophos" and "Monotrematum". The bone itself measures a total length of 46 mm, though the authors point out that it is likely missing around an eighth of its true length and suffers from some amount of abrasion, and estimate the original length at around 50 mm in life.
Kryoryctes | Morphology
Neck: Shoulder: Vertebral column: Knee
Accessory bone | Other locations
This system had evolved independently within several different amphibian lineages. The impedance matching ear had to meet certain conditions to work. The stapes had to be perpendicular to the tympanum, small and light enough to reduce its inertia, and suspended in an air-filled cavity. In modern species that are sensitive to over 1 kHz frequencies, the footplate of the stapes is 1/20th the area of the tympanum. However, in early amphibians the stapes was too large, making the footplate area oversized, preventing the hearing of high frequencies. So it appears they could only hear high intensity, low frequency sounds—and the stapes more probably just supported the brain case against the cheek.
Tetrapod | Hearing
The shape of the body is elongate and narrow. Rhinophoral sheaths are elevated with an irregular edge. Cerata are relatively short and branched. Edge of the oral veil is with relatively long appendages. Rhinophores are long and branched. Background color is translucent gray with a distinctive reticulate network of opaque white across the dorsum. It is up to 11 mm long.
Tritonia bayeri | Description
There are two hierarchical structures on the microscale. The first, at a scale of 100 μm to 1 mm, is inside the compact bone where cylindrical units called osteons and small struts can be distinguished. The second hierarchical structure, the ultrastructure, at a scale of 5 to 10 μm, is the actual structure of the osteons and small struts.
Mineralized tissues | The microscale
It is divided into the following parts: Two sphenoidal conchae are situated at the anterior and inferior part of the body.
Sphenoid bone | Structure
The rest of the body was covered by long, strap-like scales behind the head shield.
Sacabambaspis | Armor
The stapes appears to be relatively constant in size in different ethnic groups. In 0.01-0.02% of people, the stapedial artery does not regress, and persists in the central foramen. In this case, a pulsatile sound may be heard in the affected ear, or there may be no symptoms at all. Rarely, the stapes may be completely absent.
Stapes | Variation
A dark red zone borders the suture, and a broader and browner band surrounds also the middle of the body whorl.
Nassarius stolatus | Description
It is around 10 cm long, the skull is pointed, with a distinct triangular profile. At least three ossified branchial arches were present. The front legs are distinctly shorter than the hind legs; the front limbs had four fingers, while the rear limbs have five.
Hylaeobatrachus | Description
There are five types of bones in the human body: long, short, flat, irregular, and sesamoid.
Bone | Types
An alisphenoid strut separates two foramina (openings) at the base of the skull, the buccinator-masticatory foramen and the foramen ovale accessorium. The pattern of grooves and foramina on the head indicates that the circulation of the arteries in the head of "T. ucucha" follows the primitive pattern. The tegmen tympani, the roof of the tympanic cavity, overlaps the suspensory process of the squamosal bone. At the back of the mandible (lower jaw), there is a capsular process to receive the root of the lower incisor, which is absent in "T. hylophilus".
Thomasomys ucucha | Description
The hand was small. For the left hindlimb, the thigh bone was long and the shin was long.
Dromicosuchus | Description of the specimen, UNC 15574
The skeletal remains as a whole were covered with thin, oblong scales.
Trihecaton | Description
The relatively small body of "Palaeopropithecus", while large compared to the modern lemur, had a great degree curve because it was smaller in stature. There is an inverse relationship between the bigger the animal and the smaller the bone degree curve. Biomechanical theory suggests that bone curvature in "Palaeopropithecus" hand bones is linked to the functional demands of the organism's environment. This is because curved phalanges, such as the phalanges of "Palaeopropithecus", are commonly associated with the gripping function needed to survive in an arboreal habitat.
Palaeopropithecus | Anatomy
A short bone is one that is cube-like in shape, being approximately equal in length, width, and thickness. The only short bones in the human skeleton are in the carpals of the wrists and the tarsals of the ankles. Short bones provide stability and support as well as some limited motion.
Anatomical terms of bone | Short bones
At Members 1 and 2, about 35% of the "P. robustus" leg or foot specimens were the same size as those in a human, 22% in a human, and the remaining 43% bigger than the former but less than a human except for KNM‐ER 1464 (an ankle bone). At Member 3, all individuals were consistent with a human. "P. robustus" sites are oddly dominated by small adults, which could be explained as heightened predation or mortality of the larger males of a group. McHenry also estimated the living height of 3 "P. robustus" specimens (male SK 82, male SK 97, and female or subadult SK 3155), by scaling down an average human to meet the estimated size of the preserved femur, as , , and respectively.
Paranthropus robustus | Size
The scapula forms the back of the shoulder girdle. In humans, it is a flat bone, roughly triangular in shape, placed on a posterolateral aspect of the thoracic cage.
Scapula | Introduction
Little anatomical information can be gleaned from the two fragmentary cervical vertebrae aside from some measurements.
Huabeisaurus | Material
Approximately in the middle of the parietal bones was a small hole known as a pineal foramen, which may have held a sensory organ known as a parietal eye. The pineal foramen is smaller in "Seymouria" than in other seymouriamorphs. The stapes, a rod-like bone which lies between the braincase and the wall of the skull, was tapered. It connected the braincase to the upper edge of the otic notch, and likely served as a conduit of vibrations received by a tympanum (eardrum) which presumably lay within the otic notch. In this way it could transmit sound from the outside world to the brain.
Seymouria | Skull
The pore size was estimated to be about 6.5 Å.
Tic110 family | Structure
The part of the skeleton that is "tucked under" (the doublure) has no sutures crossing it to form a rostral plate. The tailshield (or pygidium) is always smaller than the headshield (or cephalon), a situation called micropygous. In the Phacopidae a merger of the anterior and the two pairs of neighbouring lobes of the glabella forms a frontal lobe that expands forward and can be inflated and overhanging the frontal border. To the back of the glabella two furrows (or sometimes one) cross the glabella forming two rings ("intercalating/pre-occipital ring" and "occipital ring"). The cephalon does not end in genal spines.
Viaphacops | Description
The tympanum is hidden, and the body is more or less laterally compressed, and covered with unequal scales. No dorsal crest is present; and a nuchal crest can be present or absent. No gular sac or gular fold is present. A large rostral appendage occurs, at least in the males. No femoral or preanal pores are found.
Ceratophora | Description
The palatine bone has an anterior process, or projection, that reaches to the level of the fourth maxillary teeth. Behind the palatine and the palatal fenestra, there are large pterygoids and ectopterygoids that project posteriorly and extend below the skull. The jugal bones, which line the side of the skull below the eyes, project laterally to form prominent ridges. The supratemporal fenestrae, two holes on the skull table, are long and narrow. There are also three ridges running longitudinally on the skull table, giving the genus its name, which means "triple-crested crocodile" in Greek. The occipital or posterior surface of the skull has structures for the insertion of muscles that would have held the head above the body.
Trilophosuchus | Description
"Hynerpeton" individuals were presumably similar to other early limbed vertebrates such as "Ichthyostega" or "Acanthostega". Although a lack of sufficient fossil material makes it unwise to come to specific conclusions about the anatomy of "Hynerpeton", the structure of the preserved endochondral shoulder girdle offers some information on its classification. The endochondral shoulder girdle is the portion of the shoulder girdle containing the scapula, coracoid, and cleithrum, but not the clavicles and interclavicle. As a whole, the endochondral shoulder girdle is massive and cleaver-shaped. The upward-pointing "shaft" is formed by the cleithrum, a blade-like bone of the shoulder girdle lost by most amniotes.
Hynerpeton | Description
In mammals, the articular and quadrate bones have migrated to the middle ear and are known as the malleus and incus. Along with the stapes, these are known as the ossicles and are a defining characteristic of mammals.
Quadrate bone | Function in mammals
The movement of the ossicles may be stiffened by two muscles. The stapedius muscle, the smallest skeletal muscle in the body, connects to the stapes and is controlled by the facial nerve; the tensor tympani muscle is attached to the upper end of the medial surface of the handle of malleus and is under the control of the medial pterygoid nerve which is a branch of the mandibular nerve of the trigeminal nerve. These muscles contract in response to loud sounds, thereby reducing the transmission of sound to the inner ear. This is called the acoustic reflex.
Middle ear | Muscles
The greater and lesser horns () are two sections of bone that project from each side of the hyoid. The greater horns project backward from the outer borders of the body; they are flattened from above downward and taper to their end, which is a bony tubercle connecting to the lateral thyrohyoid ligament. The upper surface of the greater horns are rough and close to its lateral border, and facilitates muscular attachment. The largest of muscles that attach to the upper surface of the greater horns are the hyoglossus and the middle pharyngeal constrictor, which extend along the whole length of the horns; the digastric muscle and stylohyoid muscle have small insertions in front of these near the junction of the body with the horns.
Hyoid bone | Horns
"Tutusius" is represented by a single bone from the shoulder girdle, the cleithrum. It tapers to a point anteroventrally and carries a single attachment scar for the scapulocoracoid, which extends along the anteroventral process, forms a v-shaped dorsal peak, and ends posteriorly in a projecting buttress. The cleithrum lacks ornament and has a distinct flexure point demarcating the obliquely sloping ventral half of the bone from the more vertical dorsal half. The blade of the cleithrum is broad and thin. It differs from all other tetrapod cleithra in the presence of a projecting posterior flange, with striated texture and a jagged margin, on the middle part of the blade.
Tutusius | Description
"Desmatosuchus" was a large quadruped upwards of 4.5 meters in length. Its vertebral column had amphicoelus centra and 3 sacral vertebrae. The scapulae had large acromion processes. The forelimbs were much shorter than the hindlimbs, with humeri less than two-thirds the length of the femurs. The pelvic girdle consisted of a long pubis with a strong symphysis in the middle, a plate-like ischium, a highly recurved ilium, and a deep, imperforate acetabulum. The femurs were relatively long and straight, the ankles crurotarsal, with calcaneal tubers that gave it large heels. Its skull was relatively small, on average about 37 centimeters long, 18 centimeters wide, and 15 centimeters high.
Desmatosuchus | Description
The front outer edge of the bone has a low and rounded ridge known as a deltopectoral crest. Knob-like structures (condyles) are present at the underside of the distal portion of the bone. The radial condyle (capitulum) at the front is sometimes smaller than the ulnar condyle (trochlea) at the middle, which connects to an additional rear-facing "entepicondyle"(which in humans is twisted inwards as the medial epicondyle). These different knobs are all somewhat continuous with each other, with no deep grooves separating each of them. The ulna and radius (lower arm bones) are also rather simple, although certain features (such as convex outermost joints) are shared with other archosauriforms.
Vancleavea | Forelimbs
Some individuals may also have additional (i.e., supernumerary) cervical ribs or lumbar vertebrae.
List of bones of the human skeleton | Introduction
Air vibrations could not set up pulsations through the skull as in a proper auditory organ. The spiracle was retained as the otic notch, eventually closed in by the tympanum, a thin, tight membrane. The hyomandibula of fish migrated upwards from its jaw supporting position, and was reduced in size to form the stapes. Situated between the tympanum and braincase in an air-filled cavity, the stapes was now capable of transmitting vibrations from the exterior of the head to the interior. Thus the stapes became an important element in an impedance matching system, coupling airborne sound waves to the receptor system of the inner ear.
Tetrapod | Hearing
Long bones are generally larger in males than in females within a given population. Muscle attachment sites on long bones are often more robust in males than in females, reflecting a difference in overall muscle mass and development between sexes. Sexual dimorphism in the long bones is commonly characterized by morphometric or gross morphological analyses.
Human skeleton | Long bones
In reptiles and amphibians, the bone is instead referred to as the "ulnare", since (at least in the most primitive fossils) it articulates with the ulna.
Triquetral bone | In animals