The ophthalmic artery is the first branch of the internal carotid artery distal to the cavernous sinus. Branches of the OA supply all the structures in the orbit as well as some structures in the nose and meninges. Occlusion of the OA or its branches can produce sight-threatening conditions; the OA emerges from the internal carotid artery just after the latter emerges from the cavernous sinus although in some cases, the OA branches just before the internal carotid exits the cavernous sinus. The OA arises from the internal carotid along the medial side of the anterior clinoid process and runs anteriorly passing through the optic canal with and inferolaterally to the optic nerve; the ophthalmic artery can pass superiorly to the optic nerve in a minority of cases. In the posterior third of the cone of the orbit, the ophthalmic artery turns medially to run along the medial wall of the orbit; the central retinal artery is the first, one of the smaller branches of the OA and runs in the dura mater inferior to the optic nerve.
About 12.5mm posterior to the globe, the central retinal artery turns superiorly and penetrates the optic nerve continuing along the center of the optic nerve entering the eye to supply the inner retinal layers. The next branch of the OA is the lacrimal artery, one of the largest, arises just as the OA enters the orbit and runs along the superior edge of the lateral rectus muscle to supply the lacrimal gland and conjunctiva; the OA turns medially giving off 1 to 5 posterior ciliary arteries that subsequently branch into the long and short posterior ciliary arteries which perforate the sclera posteriorly in the vicinity of the optic nerve and macula to supply the posterior uveal tract. In the past, anatomists made little distinction between the posterior ciliary arteries and the short and long posterior ciliary arteries using the terms synonymously. However, recent work by Hayreh has shown that there is both an anatomic and clinically useful distinction; the PCAs arise directly from the OA and are end arteries, to say no PCA or any of its branches anastomose with any other artery.
Sudden occlusion of any PCA will produce an infarct in the region of the choroid supplied by that particular PCA. Occlusion of a short or long PCA will produce a smaller choroidal infarct within the larger area supplied by the specific parent PCA; the OA continues medially the superior and inferior muscular branches arise either from the OA or a single trunk from the OA subsequently divides into superior and inferior branches to supply the extraocular muscles. The supraorbital artery branches from the OA as it passes over the optic nerve; the supraorbital artery passes anteriorly along the medial border of the superior rectus and levator palpebrae and through the supraorbital foramen to supply muscles and skin of the forehead. After reaching the medial wall of the orbit, the OA again turns anteriorly; the posterior ethmoidal artery enters the nose via the posterior ethmoidal canal and supplies the posterior ethmoidal sinuses and enters the skull to supply the meninges. The OA continues anteriorly, giving off the anterior ethmoidal artery which enters the nose after traversing the anterior ethmoidal canal and supplies the anterior and middle ethmoidal sinuses as well as the frontal sinus and enters the cranium to supply the meninges.
The OA continues anteriorly to the trochlea where the medial palpebral arteries arise and supply the eyelids. The OA terminates in the supratrochlear artery and the dorsal nasal artery. Both exit the orbit medially to supply the scalp; because of the obvious importance of the ocular globe, branches of the ophthalmic artery are subdivided into two groups: those that supply the eyeball and those that supply non-ocular orbital structures. The orbital group, distributing vessels to the orbit and surrounding parts, includes: Lacrimal artery A. lacrimalis Supraorbital artery A. supraorbitalis Posterior ethmoidal artery A. ethmoidalis posterior Anterior ethmoidal artery A. ethmoidalis anterior Medial palpebral artery A. palpebralis medialis Frontal artery called the Supratrochlear artery A. supratrochlearis Dorsal nasal artery A. dorsalis nasi The ocular group, distributing vessels to the eye and its muscles, includes: Long posterior ciliary arteries Aa. ciliares posteriores longae Short posterior ciliary arteries Aa. ciliares posteriores breves Anterior ciliary artery A. ciliares anterior Central retinal artery A. centralis retinae Superior muscular artery A. supraorbitalis Inferior muscular artery A. infraorbitalis Branches of the ophthalmic artery supply: Frontal belly of the occipitofrontalis muscle Inferior oblique muscle Inferior rectus muscle Lacrimal gland Lateral rectus muscle Levator palpebrae superioris muscle Medial rectus muscle Nasalis muscle Procerus muscle Superior oblique muscle Superior rectus muscle Severe occlusion of the ophthalmic artery causes ocular ischemic syndrome.
As with central retinal artery occlusions, ophthalmic artery occlusions may result from systemic cardiovascular diseases. Amaurosis fugax is a temporary loss of vision that occurs in two conditions which cause a temporary reduction in ophthalmic artery pressure: orthostatic hypotension and positive acceleration. Complete occlusion of the ophthalmic artery may leave the eye without symptoms because of circulatory anastomoses Fluorescein angiography MedEd at Loyola Neuro/neurovasc/navigation/opht.htm Anatomy photo:29:03-0102 at the SUNY Downstate Medical Center "Ophthalmic Artery | neuroangio.org". Neuroangio.org. Retrieved 2015-10-23
The human eye is an organ which reacts to light and pressure. As a sense organ, the mammalian eye allows vision. Human eyes help to provide a three dimensional, moving image coloured in daylight. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth; the human eye can differentiate between about 10 million colors and is capable of detecting a single photon. Similar to the eyes of other mammals, the human eye's non-image-forming photosensitive ganglion cells in the retina receive light signals which affect adjustment of the size of the pupil and suppression of the hormone melatonin and entrainment of the body clock; the eye is not shaped like a perfect sphere, rather it is a fused two-piece unit, composed of the anterior segment and the posterior segment. The anterior segment is made up of the cornea and lens; the cornea is transparent and more curved, is linked to the larger posterior segment, composed of the vitreous, retina and the outer white shell called the sclera.
The cornea is about 11.5 mm in diameter, 1/2 mm in thickness near its center. The posterior chamber constitutes the remaining five-sixths; the cornea and sclera are connected by an area termed the limbus. The iris is the pigmented circular structure concentrically surrounding the center of the eye, the pupil, which appears to be black; the size of the pupil, which controls the amount of light entering the eye, is adjusted by the iris' dilator and sphincter muscles. Light energy enters the eye through the cornea, through the pupil and through the lens; the lens shape is controlled by the ciliary muscle. Photons of light falling on the light-sensitive cells of the retina are converted into electrical signals that are transmitted to the brain by the optic nerve and interpreted as sight and vision. Dimensions differ among adults by only one or two millimetres, remarkably consistent across different ethnicities; the vertical measure less than the horizontal, is about 24 mm. The transverse size of a human adult eye is 24.2 mm and the sagittal size is 23.7 mm with no significant difference between sexes and age groups.
Strong correlation has been found between the width of the orbit. The typical adult eye has an anterior to posterior diameter of 24 millimetres, a volume of six cubic centimetres, a mass of 7.5 grams.. The eyeball grows increasing from about 16–17 millimetres at birth to 22.5–23 mm by three years of age. By age 12, the eye attains its full size; the eye is made up of layers, enclosing various anatomical structures. The outermost layer, known as the fibrous tunic, is composed of the sclera; the middle layer, known as the vascular tunic or uvea, consists of the choroid, ciliary body, pigmented epithelium and iris. The innermost is the retina, which gets its oxygenation from the blood vessels of the choroid as well as the retinal vessels; the spaces of the eye are filled with the aqueous humour anteriorly, between the cornea and lens, the vitreous body, a jelly-like substance, behind the lens, filling the entire posterior cavity. The aqueous humour is a clear watery fluid, contained in two areas: the anterior chamber between the cornea and the iris, the posterior chamber between the iris and the lens.
The lens is suspended to the ciliary body by the suspensory ligament, made up of hundreds of fine transparent fibers which transmit muscular forces to change the shape of the lens for accommodation. The vitreous body is a clear substance composed of water and proteins, which give it a jelly-like and sticky composition; the approximate field of view of an individual human eye varies by facial anatomy, but is 30° superior, 45° nasal, 70° inferior, 100° temporal. For both eyes combined visual field is 200 ° horizontal, it is 13700 square degrees for binocular vision. When viewed at large angles from the side, the iris and pupil may still be visible by the viewer, indicating the person has peripheral vision possible at that angle. About 15° temporal and 1.5° below the horizontal is the blind spot created by the optic nerve nasally, 7.5° high and 5.5° wide. The retina has a static contrast ratio of around 100:1; as soon as the eye moves to acquire a target, it re-adjusts its exposure by adjusting the iris, which adjusts the size of the pupil.
Initial dark adaptation takes place in four seconds of profound, uninterrupted darkness. The process is nonlinear and multifaceted, so an interruption by light exposure requires restarting the dark adaptation process over again. Full adaptation is dependent on good blood flow; the human eye can detect a luminance range of 1014, or one hundred trillion, from 10−6 cd/m2, or one millionth of a candela per square meter to 108 cd/m2 or one hundred million candelas per square meter. This range does not include looking at the midday lightning discharge. At the low end o
The Pekingese is an ancient breed of toy dog, originating in China. They are called Lion Dogs due to their resemblance to Chinese guardian lions. Another breed, the Shih Tzu, has its English name derive from the same source as this breed's Chinese name which translates to "lion dog"; the breed was favored by royalty of the Chinese Imperial court as both a lap dog and companion dog, its name refers to the city of Peking where the Forbidden City is located. The breed has several characteristics and health issues related to its unique appearance; because of its desirable characteristics, the Pekingese has been part of the development of designer crossbreeds, such as the Peekapoo and Peke-a-tese. The breed originated in Western China in antiquity. Recent DNA analysis confirms that the Pekingese breed is one of the oldest breeds of dog, one of the least genetically diverged from the wolf; the Pekingese breed has hardly changed in all that time. One exception is that modern breeders and dog show judges seem to prefer the long-haired type over the more traditional spaniel-type coat.
The Pekingese's flat face and large eyes are some of the breeds most obvious characteristics. The body is low to the ground. Pekingese have a muscular and durable body; the breed's unusual rolling gait may have been deliberately developed by breeding to prevent the court dogs from wandering in ancient times. All breed standards allow a wide range of color combinations; the majority of Pekingese are red or sable. Cream, white, tan and tan and occasionally'blue' or slate grey have appeared in the breed; the latter has poor pigment and light eyes. Albino Pekingese should be bred cautiously due to health problems that have been associated with albinism; the Pekingese sheds a lot. A black mask or a self-colored face is acceptable in show dogs. Regardless of coat color, the exposed skin of the muzzle, nose and eye rims is black, they require a lot of grooming. The Pekingese weigh from 7 to 14 lb and stand about 6–9 inches at the withers, however they can sometimes be smaller; these smaller Pekingese are referred to as "Sleeve" Pekingese or just "Sleeves".
The name is taken from ancient times, when emperors would carry the smallest of the breed in their sleeves. A Pekingese over 15 pounds is disqualified in the show ring; the Pekingese is longer than tall when measured from the forechest to the buttocks. The overall outline is an approximate ratio of 3 high to 5 long; the Pekingese has a median lifespan of 11.4 years in a UK Kennel Club survey. The leading cause of death for Pekingese, as for many other Toy breeds, is trauma. Top leading causes of organ systems include neurologic and cardiovascular, e.g. congestive heart failure. When diagnosed early and treated with medication, a Pekingese with this problem can expect to live many years. A heart murmur is a potential sign of a problem, must be evaluated by a veterinary cardiologist; the problem does not surface until the dog is 6 or more years old, so it is difficult to screen the problem in a pup. The other main problems of the breed are eye issues and breathing problems, resulting from its tiny skull and flattened face, skin allergies.
An common problem is eye ulcers, which may develop spontaneously. Pekingese may develop keratoconjunctivitis sicca progressive retinal atrophy, along with glaucoma in which pressure is placed on the eye, leading to fluid drainage in the eye; the leading cause of this is improper development of the eye's filtration angles. The Pekingese should not be kept outside, as having flattened faces and noses can cause them to develop breathing problems, making it difficult for them to regulate their body temperature in overly hot or cold weather, their long backs, relative to their legs, make them vulnerable to back injuries. Care should be taken when picking them up to give adequate support to the back: one hand under the chest, the other under the abdomen. Short legs give some Pekingese difficulty with stairs. In an effort to address the breathing difficulties caused by the breed's flat face, the Kennel Club changed the breed standard in October 2008, removing the clause that the "profile flat with nose well up between eyes" and adding instead that the "muzzle must be evident".
This was in response to public opinion following Pedigree Dogs Exposed. The breed standards of two other flat-faced breeds, the Pug and English Bulldog, were soon changed. Keeping the Pekingese coat healthy and presentable requires daily brushing, a trip to the groomer every 8–12 weeks. One important thing for new owners to remember is that dogs intended as a house pet may be kept in a puppy cut which requires less maintenance than a show cut, it is important to remove foreign materials from the eyes daily, the creases on the face to prevent sores. It is necessary to keep and maintain the fur in the buttocks of the Pekingese clean and well groomed as the area is prone to soiling. Due to their abundance of fur, it is important to keep the Pekingese cool; the breed is prone to have heatstroke. Pekingese exercise needs are minimal. Due to their short snouts, they tend to have a high risk for breathing difficulties; because of this, around 30 minutes of exercise per day is enough to keep them healthy.
It is important to monitor their breathing while exercising
The extraocular muscles are the six muscles that control movement of the eye and one muscle that controls eyelid elevation. The actions of the six muscles responsible for eye movement depend on the position of the eye at the time of muscle contraction. Since only a small part of the eye called the fovea provides sharp vision, the eye must move to follow a target. Eye movements must be fast; this is seen in scenarios like reading. Although under voluntary control, most eye movement is accomplished without conscious effort. How the integration between voluntary and involuntary control of the eye occurs is a subject of continuing research, it is known, that the vestibulo-ocular reflex plays an important role in the involuntary movement of the eye. Four of the extraocular muscles have their origin in the back of the orbit in a fibrous ring called the annulus of Zinn: the four rectus muscles; the four rectus muscles attach directly to the front half of the eye, are named after their straight paths. Note that medial and lateral are relative terms.
Medial indicates near the midline, lateral describes a position away from the midline. Thus, the medial rectus is the muscle closest to the nose; the superior and inferior recti do not pull straight back on the eye, because both muscles pull medially. This posterior medial angle causes the eye to roll with contraction of either the superior rectus or inferior rectus muscles; the extent of rolling in the recti is less than the oblique, opposite from it. The superior oblique muscle originates at the back of the orbit, getting rounder as it courses forward to a rigid, cartilaginous pulley, called the trochlea, on the upper, nasal wall of the orbit; the muscle becomes tendinous about 10mm before it passes through the pulley, turning across the orbit, inserts on the lateral, posterior part of the globe. Thus, the superior oblique travels posteriorly for the last part of its path, going over the top of the eye. Due to its unique path, the superior oblique, when activated, pulls the eye laterally; the last muscle is the inferior oblique, which originates at the lower front of the nasal orbital wall, passes under the LR to insert on the lateral, posterior part of the globe.
Thus, the inferior oblique pulls the eye laterally. The movements of the extraocular muscles take place under the influence of a system of extraocular muscle pulleys, soft tissue pulleys in the orbit; the extraocular muscle pulley system is fundamental to the movement of the eye muscles, in particular to ensure conformity to Listing's law. Certain diseases of the pulleys cause particular patterns of incomitant strabismus. Defective pulley functions can be improved by surgical interventions; the extraocular muscles are supplied by branches of the ophthalmic artery. This is done either directly or indirectly, as in the lateral rectus muscle, via the lacrimal artery, a main branch of the ophthalmic artery. Additional branches of the ophthalmic artery include the ciliary arteries, which branch into the anterior ciliary arteries; each rectus muscle receives blood from two anterior ciliary arteries, except for the lateral rectus muscle, which receives blood from only one. The exact number and arrangement of these cilary arteries may vary.
Branches of the infraorbital artery supply inferior oblique muscles. The nuclei or bodies of these nerves are found in the brain stem; the nuclei of the abducens and oculomotor nerves are connected. This is important in coordinating the motion of the lateral rectus in one eye and the medial action on the other. In one eye, in two antagonistic muscles, like the lateral and medial recti, contraction of one leads to inhibition of the other. Muscles show small degrees of activity when resting, keeping the muscles taut; this "tonic" activity is brought on by discharges of the motor nerve to the muscle. The extraocular muscles develop along with the fatty tissue of the eye socket. There are three centers of growth that are important in the development of the eye, each is associated with a nerve. Hence the subsequent nerve supply of the eye muscles is from three cranial nerves; the development of the extraocular muscles is dependent on the normal development of the eye socket, while the formation of the ligament is independent.
Below is a table of each of the extraocular muscles and their innervation and insertions, the primary actions of the muscles. Intermediate directions are controlled by simultaneous actions of multiple muscles; when one shifts the gaze horizontally, one eye will move laterally and the other will move medially. This may be neurally coordinated by the central nervous system, to make the eyes move together and involuntarily; this is a key factor in the study of strabismus, the inability of the eyes to be directed to one point. There are two main kinds of movement: disjunctive; the former is typical when shifting gaze right or left, the latter is convergence of the two eyes on a near object. Disjunction can be performed voluntarily, but is triggered by the nearness of the target object. A "see-saw" movement, one eye looking up and the other down, is possible, but not voluntarily. To avoi
Pupillary light reflex
The pupillary light reflex or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity of light that falls on the retinal ganglion cells of the retina in the back of the eye, thereby assisting in adaptation to various levels of lightness/darkness. A greater intensity of light causes the pupil to constrict, whereas a lower intensity of light causes the pupil to dilate. Thus, the pupillary light reflex regulates the intensity of light entering the eye. Light shone into one eye will cause both pupils to constrict. Pupil is where light enters the eye. Based on analogy with a camera, pupil is equivalent to aperture, whereas iris is equivalent to the diaphragm. Pupillary reflex should have been named iris reflex, because iris is the actual muscular structure that responds to light and pupil is the passive opening formed by the active iris. Pupillary reflex is synonymous with pupillary response, which may be pupillary constriction or dilation. Pupillary reflex is conceptually linked to the side of the reacting pupil, not to the side from which light stimulation originates.
Left pupillary reflex refers to the response of the left pupil to light, regardless of which eye is exposed to a light source. Right pupillary reflex means reaction of the right pupil, whether light is shone into the left eye, right eye, or both eyes. In contrast, the terms direct and consensual refers to the side where the light source comes from, relative to the side of the reacting pupil. A direct pupillary reflex is pupillary response to light. A consensual pupillary reflex is response of a pupil to light, thus there are four types of pupillary light reflexes, based on this terminology of absolute and relative laterality: Left direct pupillary reflex is the left pupil's response to light entering the left eye, the ipsilateral eye. Left consensual pupillary reflex is the left pupil's indirect response to light entering the right eye, the contralateral eye. Right direct pupillary reflex is the right pupil's response to light entering the right eye, the ipsilateral eye. Right consensual pupillary reflex is the right pupil's indirect response to light entering the left eye, the contralateral eye.
The pupillary light reflex neural pathway on each side has two efferent limbs. The afferent limb has nerve fibers running within the optic nerve; each efferent limb has nerve fibers running along the oculomotor nerve. The afferent limb carries sensory input. Anatomically, the afferent limb consists of the retina, the optic nerve, the pretectal nucleus in the midbrain, at level of superior colliculus. Ganglion cells of the retina project fibers through the optic nerve to the ipsilateral pretectal nucleus; the efferent limb is the pupillary motor output from the pretectal nucleus to the ciliary sphincter muscle of the iris. The pretectal nucleus projects crossed and uncrossed fibers to the ipsilateral and contralateral Edinger-Westphal nuclei, which are located in the midbrain; each Edinger-Westphal nucleus gives rise to preganglionic parasympathetic fibers which exit with CN III and synapse with postganglionic parasympathetic neurons in the ciliary ganglion. Postganglionic nerve fibers leave the ciliary ganglion to innervate the ciliary sphincter.
Each afferent limb has one ipsilateral and one contralateral. The ipsilateral efferent limb transmits nerve signals for direct light reflex of the ipsilateral pupil; the contralateral efferent limb causes consensual light reflex of the contralateral pupil. The optic nerve, or more the photosensitive ganglion cells through the retinohypothalamic tract, is responsible for the afferent limb of the pupillary reflex; the oculomotor nerve is responsible for the efferent limb of the pupillary reflex. Retina: The pupillary reflex pathway begins with the photosensitive retinal ganglion cells, which convey information via the optic nerve, the most peripheral, portion of, the optic disc; some axons of the optic nerve connect to the pretectal nucleus of the upper midbrain instead of the cells of the lateral geniculate nucleus. These intrinsic photosensitive ganglion cells are referred to as melanopsin-containing cells, they influence circadian rhythms as well as the pupillary light reflex. Pretectal nuclei: From the neuronal cell bodies in some of the pretectal nuclei, axons synapse on neurons in the Edinger-Westphal nucleus.
Those neurons are the preganglionic cells with axons that run in the oculomotor nerves to the ciliary ganglia. Edinger-Westphal nuclei: Parasympathetic neuronal axons in the oculomotor nerve synapse on ciliary ganglion neurons. Ciliary ganglia: Short post-ganglionic ciliary nerves leave the ciliary ganglion to innervate the Iris sphincter muscle of the iris; the pupillary response to light is not purely reflexive, but is modulated by cognitive factors, such as attention and the way visual input is interpreted. For example, if a bright stimulus is presented to one eye, a dark stimulus to the other eye, perception alternates between the two eyes: Sometimes the dark stimulus is perceived, sometimes the bright stimulus, but never both at the same time. Using this technique, it has been shown the pupil is smaller when a bright stimulus dominates awareness, relative to when a dark stimulus dominates awareness; this shows t
Anatomical terms of location
Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. All vertebrates have the same basic body plan – they are bilaterally symmetrical in early embryonic stages and bilaterally symmetrical in adulthood; that is, they have mirror-image left and right halves if divided down the middle. For these reasons, the basic directional terms can be considered to be those used in vertebrates. By extension, the same terms are used for many other organisms as well. While these terms are standardized within specific fields of biology, there are unavoidable, sometimes dramatic, differences between some disciplines. For example, differences in terminology remain a problem that, to some extent, still separates the terminology of human anatomy from that used in the study of various other zoological categories. Standardized anatomical and zoological terms of location have been developed based on Latin and Greek words, to enable all biological and medical scientists to delineate and communicate information about animal bodies and their component organs though the meaning of some of the terms is context-sensitive.
The vertebrates and Craniata share a substantial heritage and common structure, so many of the same terms are used for location. To avoid ambiguities this terminology is based on the anatomy of each animal in a standard way. For humans, one type of vertebrate, anatomical terms may differ from other forms of vertebrates. For one reason, this is because humans have a different neuraxis and, unlike animals that rest on four limbs, humans are considered when describing anatomy as being in the standard anatomical position, thus what is on "top" of a human is the head, whereas the "top" of a dog may be its back, the "top" of a flounder could refer to either its left or its right side. For invertebrates, standard application of locational terminology becomes difficult or debatable at best when the differences in morphology are so radical that common concepts are not homologous and do not refer to common concepts. For example, many species are not bilaterally symmetrical. In these species, terminology depends on their type of symmetry.
Because animals can change orientation with respect to their environment, because appendages like limbs and tentacles can change position with respect to the main body, positional descriptive terms need to refer to the animal as in its standard anatomical position. All descriptions are with respect to the organism in its standard anatomical position when the organism in question has appendages in another position; this helps avoid confusion in terminology. In humans, this refers to the body in a standing position with arms at the side and palms facing forward. While the universal vertebrate terminology used in veterinary medicine would work in human medicine, the human terms are thought to be too well established to be worth changing. Many anatomical terms can be combined, either to indicate a position in two axes or to indicate the direction of a movement relative to the body. For example, "anterolateral" indicates a position, both anterior and lateral to the body axis. In radiology, an X-ray image may be said to be "anteroposterior", indicating that the beam of X-rays pass from their source to patient's anterior body wall through the body to exit through posterior body wall.
There is no definite limit to the contexts in which terms may be modified to qualify each other in such combinations. The modifier term is truncated and an "o" or an "i" is added in prefixing it to the qualified term. For example, a view of an animal from an aspect at once dorsal and lateral might be called a "dorsolateral" view. Again, in describing the morphology of an organ or habitus of an animal such as many of the Platyhelminthes, one might speak of it as "dorsiventrally" flattened as opposed to bilaterally flattened animals such as ocean sunfish. Where desirable three or more terms may be agglutinated or concatenated, as in "anteriodorsolateral"; such terms sometimes used to be hyphenated. There is however little basis for any strict rule to interfere with choice of convenience in such usage. Three basic reference planes are used to describe location; the sagittal plane is a plane parallel to the sagittal suture. All other sagittal planes are parallel to it, it is known as a "longitudinal plane".
The plane is perpendicular to the ground. The median plane or midsagittal plane is in the midline of the body, divides the body into left and right portions; this passes through the head, spinal cord, and, in many animals, the tail. The term "median plane" can refer to the midsagittal plane of other structures, such as a digit; the frontal plane or coronal plane divides the body into ventral portions. For post-embryonic humans a coronal plane is vertical and a transverse plane is horizontal, but for embryos and quadrupeds a coronal plane is horizontal and a transverse plane is vertical. A longitudinal plane is any plane perpendicular to the transverse plane; the coronal plane and the sagittal plane are examples of longitudinal planes. A transverse plane known as a cross-section, divides the body into cranial and caudal portions. In human anatomy: A transverse plane is an X-Z plane, parallel to the ground, which s
The domestic dog is a member of the genus Canis, which forms part of the wolf-like canids, is the most abundant terrestrial carnivore. The dog and the extant gray wolf are sister taxa as modern wolves are not related to the wolves that were first domesticated, which implies that the direct ancestor of the dog is extinct; the dog was the first species to be domesticated and has been selectively bred over millennia for various behaviors, sensory capabilities, physical attributes. Their long association with humans has led dogs to be uniquely attuned to human behavior and they are able to thrive on a starch-rich diet that would be inadequate for other canid species. Dogs vary in shape and colors, they perform many roles for humans, such as hunting, pulling loads, assisting police and military, companionship and, more aiding disabled people and therapeutic roles. This influence on human society has given them the sobriquet of "man's best friend"; the term dog is applied both to the species as a whole, any adult male member of the same.
An adult female is a bitch. An adult male capable of reproduction is a stud. An adult female capable of reproduction is brood mother. Immature males or females are puppies. A group of pups from the same gestation period is called a litter; the father of a litter is a sire. It is possible for one litter to have multiple sires; the mother of a litter is a dam. A group of any three or more adults is a pack. In 1999, a study of mitochondrial DNA indicated that the domestic dog may have originated from multiple grey wolf populations, with the dingo and New Guinea singing dog "breeds" having developed at a time when human populations were more isolated from each other. In the third edition of Mammal Species of the World published in 2005, the mammalogist W. Christopher Wozencraft listed under the wolf Canis lupus its wild subspecies, proposed two additional subspecies: "familiaris Linneaus, 1758 " and "dingo Meyer, 1793 ". Wozencraft included hallstromi – the New Guinea singing dog – as a taxonomic synonym for the dingo.
Wozencraft referred to the mDNA study as one of the guides in forming his decision. The inclusion of familiaris and dingo under a "domestic dog" clade has been noted by other mammalogists; this classification by Wozencraft is debated among zoologists. The origin of the domestic dog includes the dog's evolutionary divergence from the wolf, its domestication, its development into dog types and dog breeds; the dog is a member of the genus Canis, which forms part of the wolf-like canids, was the first species and the only large carnivore to have been domesticated. The dog and the extant gray wolf are sister taxa, as modern wolves are not related to the population of wolves, first domesticated; the genetic divergence between dogs and wolves occurred between 40,000–20,000 years ago, just before or during the Last Glacial Maximum. This timespan represents the upper time-limit for the commencement of domestication because it is the time of divergence and not the time of domestication, which occurred later.
The domestication of animals commenced over 15,000 years ago, beginning with the grey wolf by nomadic hunter-gatherers. The archaeological record and genetic analysis show the remains of the Bonn–Oberkassel dog buried beside humans 14,200 years ago to be the first undisputed dog, with disputed remains occurring 36,000 years ago, it was not until 11,000 years ago that people living in the Near East entered into relationships with wild populations of aurochs, boar and goats. Where the domestication of the dog took place remains debated, with the most plausible proposals spanning Western Europe, Central Asia and East Asia; this has been made more complicated by the recent proposal that an initial wolf population split into East and West Eurasian groups. These two groups, before going extinct, were domesticated independently into two distinct dog populations between 14,000 and 6,400 years ago; the Western Eurasian dog population was and replaced by East Asian dogs introduced by humans at least 6,400 years ago.
This proposal is debated. Domestic dogs have been selectively bred for millennia for various behaviors, sensory capabilities, physical attributes. Modern dog breeds show more variation in size and behavior than any other domestic animal. Dogs are predators and scavengers, like many other predatory mammals, the dog has powerful muscles, fused wrist bones, a cardiovascular system that supports both sprinting and endurance, teeth for catching and tearing. Dogs are variable in height and weight; the smallest known adult dog was a Yorkshire Terrier, that stood only 6.3 cm at the shoulder, 9.5 cm in length along the head-and-body, weighed only 113 grams. The largest known dog was an English Mastiff which weighed 155.6 kg and was 250 cm from the snout to the tail. The tallest dog is a Great Dane; the dog's senses include vision, sense of smell, sense of taste and sensitivity to the earth's magnetic field. Another study suggested; the coats of domestic dogs are of two varieties: "double" being common with dogs originating from colder climates, made up of a coarse guard hair and a soft down hair, or "single", with the topcoat only.
Breeds may have stripe, or "star" of white fur on their chest or underside. Regarding coat appearance or h