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Front versus back in animal anatomy


Throughout various species, there seems to be a clear distinction between the front and the back. The musculature of the front, when engaged, closes or curls up the body, protecting it, while the musculature of the front straightens and stiffens. This feels intuitively to me like a pretty fundamental pattern.

Is this a "real" pattern at an embryological level, or just a common pattern of adaptation?

Is the innervation of the front and back musculature neurologically distinct in any way?

Which biological systems show a front to back separation?

How early in evolution does a front to back distinction occur?


What is Anterior and Posterior?

Anterior is the anatomical term for indicating that an organ or structure is towards the front of the body. It is usually used to indicate the position in relation to another organ or structure and may mean that it is ‘in front of’ another organ or structure.

For example – in a person who is standing erect, the tip of the nose is anterior to the eyes meaning that the nose tip is in front of or located before the eyes.

The term anterior may also be used to indicate ‘towards the head’ because isolating the front and rear (posterior) orientation may be misleading in certain situations, especially in certain animals.

To prevent ambiguity, anterior is regarded as the position towards the front or in front of another organ or structure when a person is in the standard anatomical position for humans (refer to picture) which is standing erect, with the feet together, upper limbs slightly away from the sides of the body with the palms facing forward and the thumb pointing away from the body.


Body Plans

Figure 1. Animals exhibit different types of body symmetry. The sponge is asymmetrical, the sea anemone has radial symmetry, and the goat has bilateral symmetry.

Animal body plans follow set patterns related to symmetry. They are asymmetrical, radial, or bilateral in form as illustrated in Figure 1. Asymmetrical animals are animals with no pattern or symmetry an example of an asymmetrical animal is a sponge. Radial symmetry, as illustrated in Figure 1, describes when an animal has an up-and-down orientation: any plane cut along its longitudinal axis through the organism produces equal halves, but not a definite right or left side. This plan is found mostly in aquatic animals, especially organisms that attach themselves to a base, like a rock or a boat, and extract their food from the surrounding water as it flows around the organism. Bilateral symmetry is illustrated in the same figure by a goat. The goat also has an upper and lower component to it, but a plane cut from front to back separates the animal into definite right and left sides. Additional terms used when describing positions in the body are anterior (front), posterior (rear), dorsal (toward the back), and ventral (toward the stomach). Bilateral symmetry is found in both land-based and aquatic animals it enables a high level of mobility.


2. From Antiquity to the Renaissance

Humans have been using other vertebrate animal species (referred to henceforth as animals) as models of their anatomy and physiology since the dawn of medicine. Because of the taboos regarding the dissection of humans, physicians in ancient Greece dissected animals for anatomical studies [1]. Prominent physicians from this period who performed “vivisections” (stricto sensu the exploratory surgery of live animals, and historically used lato sensu as a depreciative way of referring to animal experiments) include Alcmaeon of Croton (6th𠄵th century BCE) [2,3], Aristotle, Diocles, Praxagoras (4th century BCE), Erasistratus, and Herophilus (4th𠄳rd century BCE) [1,3,4]. The latter two were Hellenic Alexandrians who disregarded the established taboos and went on to perform dissection and vivisection on convicted criminals, benefiting from the favorable intellectual and scientific environment in Alexandria at the time [1]. All of these authors had a great influence on Galen of Pergamon (2nd𠄳rd century CE), the prolific Roman physician of Greek ethnicity who developed, to an unprecedented level, the techniques for dissection and vivisection of animals [3,5] and on which he based his many treatises of medicine. These remained canonical, authoritative, and undisputed until the Renaissance [1,6].

For most ancient Greeks, using live animals in experiments did not raise any relevant moral questions. The supposed likeliness of humans to their anthropomorphic deities granted them a higher ranking in the scala naturae (“the chain of being”), a strict hierarchy where all living and non-living natural things𠅏rom minerals to the gods—were ranked according to their proximity to the divine. This view of humans as superior would later influence and underline the Judeo-Christian perspective of human dominion over all nature, as represented by texts by Augustine of Hippo (IV century) and Thomas Aquinas (XIII Century), the most influential Christian theologians of the Middle Ages. For Augustine, animals were part of a natural world created to serve humans (as much as the �rth, water and sky”) and humankind did not have any obligations to them. For Thomas Aquinas, the mistreatment of another person’s animal would be sinful, not for the sake of the animal in itself, but because it is someone else’s property. Cruelty to animals was nevertheless condemned by Aquinas, as it could lead humans to develop feelings and actions of cruelty towards other humans. Also, for this theologian, one could love irrational creatures for the sake of charity, the love of God and the benefit of fellow humans (for selected texts, see reference [7]).

The belief amongst ancient Greek physicians that nature could be understood by means of exploration and experiment𠅊nd the medical knowledge thus obtained to be of clinical relevance in practice—would be replaced by other schools of medical thought. Most notably, the Empiric school (3rd century BCE𠄴th century) would reject the study of anatomy and physiology by dissection of cadavers or by vivisection, not only on the grounds of cruelty and the established taboos, but also for its uselessness. Empiricists believed pain and death would distort the normal appearance of internal organs and criticized the speculative nature of the conclusions drawn from experiments. Indeed, and despite taking an experimental approach to understand the human body and illness, the interpretations of physiological processes made by ancient Greeks who performed vivisections were often inaccurate. The theoretical frameworks by which physicians interpreted their experiments more often than not led them to misguided conclusions. Observations would be understood in light of such paradigms as the Hippocratic theory of the four humors or the Pythagorean theory of the four elements, along with others of natural or supernatural basis, and to which they added their own theoretical conceptions and observational errors [1,4,6,8,9]. The study of human or animal anatomy and physiology was hence deemed irrelevant for clinical practice. Beginning with the decline of the Roman Empire and continuing throughout the Middle Ages, physiological experiments𠅊long with scientific activity in general—would fall almost entirely into disuse and medical knowledge would become dogmatic. In an increasingly Christianized Europe, there was little motivation to pursue scientific advancement of medical knowledge, as people became more concerned with eternal life than with worldly life, and returned to Pre-Hippocratic beliefs in supernatural causes for disease and in the healing power of faith and superstition. Therefore, and despite medieval physicians’ reverence for Galen and his predecessors, the experimental approach used by these classical authors had been sentenced to oblivion [3,8,9,10,11].

The use of animal experiments to satisfy scientific enquiry would only re-emerge in the Renaissance. Flemish anatomist Vesalius (1514�), through the course of his work as a physician and surgeon, realized that many anatomical structures thought to exist in humans—on account of them being present in other animals—were in fact absent [6]. This led him to break the established civil and religious rules and dissect illegally obtained human cadavers, and publish very accurate descriptions of the human anatomy, which challenged the authority of the classical authors. As Herophilus did centuries before (but not carried on by his successors) [1] Vesalius would also examine the similarities and differences between the internal structure of humans and other animals, thus setting the foundations of modern comparative anatomy.

Alongside the progress in anatomical knowledge made possible by experimenters defying the Catholic Church’s opposition to the dissection of human bodies, the Renaissance period also witnessed the resurgence of vivisection as a heuristic method for the understanding of animal physiology. Vesalius would again recognize the value of physiological experiments on animals as both a learning and teaching resource—he would vivisect animals for medical students as the finishing touch at the end of his courses𠅊 view shared by his contemporary, and presumable student and rival, Realdo Colombo (1516�) [3]. Later, Francis Bacon (1561�), considered by many the founder of modern scientific methodology, would also approve of the scientific relevance of vivisection, stating that “the inhumanity of anatomia vivorum was by Celsus justly reproved yet in regard of the great use of this observation, the inquiry needed (…) might have been well diverted upon the dissection of beasts alive, which notwithstanding the dissimilitude of their parts may sufficiently satisfy this inquiry” [12].


Front versus back in animal anatomy - Biology

Maltese can be very energetic, despite this they still do well for apartment dwellers. They are relatively easy to train and enjoy a playful game of fetch. These intelligent dogs learn quickly, and pick up new tricks and behaviors easily. Characteristics include slightly rounded skulls, with a one-finger-wide dome and a black nose that is two finger widths long. The body is compact with the length equaling the height. The drop ears with long hair and very dark eyes, surrounded by darker skin pigmentation that is called a "halo", gives Maltese their expressive look. Their noses can fade and become pink or light brown in color. This is often referred to as a "winter nose" and many times will become black again with increased exposure to the sun.

The coat is long and silky and lacks an undercoat. The color is pure white and although cream or light lemon ears are permissible, they are not desirable. Some individuals may have curly or woolly hair, but this is outside the standard. The Maltese while growing may get curly fur. They are very cute. Adult Maltese range from roughly(1.4 to 3.0 kg, though breed standards, as a whole, call for weights between 1.8 to 3. kg. There are variations depending on which standard is being used many, like the American Kennel Club, call for a weight that is ideally less than 7 lb with between 4 and 6 lb preferred.

For all their diminutive size, Maltese seem to be without fear. In fact, many Maltese seem relatively indifferent to creatures/objects larger than themselves, which makes them very easy to socialize with other dogs, and even cats. They are always happy, cheerful, smart and do not like to get into trouble. They tend to get very lonely if the master is not with them and taken care of and it doesn't like being left out. This is because they were bred to be companion dogs and thrive on love and attention. They are extremely lively and playful, and even as a Maltese ages, his/her energy level and playful demeanor remain fairly constant and does not diminish much.

Maltese are very good with children and infants. Maltese can sometimes be snappy and mean. Maltese do not require much physical exercise, although they should be walked daily to reduce problem behavior. They enjoy running and are more inclined to play games of chase, rather than play with toys. Maltese can be snappy with littler children and should always be supervised when playing. Socializing at a young age will reduce this habit. They can be very demanding and, true to their nature as "lap dogs", love to cuddle and often seek this sort of attention. The Maltese is very active in the house, and, preferring enclosed spaces, does very well with small yards. For this reason the breed also does well with apartments and townhouses, and is a prized pet of urban dwellers. They are incredibly friendly dogs to people they know. With strangers they will make a high pitched bark but will quiet down if the person means no harm.


How Fleas Work

Fleas are minuscule, but anyone who has seen one usually can recognize it with ease. They're tiny, flat, wingless insects that have a knack for jumping away before you can catch them. Their bodies are covered with hard plates called sclerites. So, if you do catch one, squashing it can be a challenge. Their hard, outer shell protects them from everything from an animal's teeth to hitting the floor after a long jump.

To the naked eye, a flea's exoskeleton seems completely smooth, but it's really covered in tiny hairs that point away from the flea's head. Their flattened bodies and these backward-pointing hairs are what enables them to crawl through a host's fur, and if something tries to dislodge them, the hairs act like tiny Velcro anchors. That's why a fine-toothed comb removes fleas better than a brush. The teeth of the comb are too close together for fleas to slip through, so it can pull them from the host's hair, regardless of which way a flea's hairs are pointing.

A flea also has spines around its head and mouth, with the number and shape varying according to the species. The mouth itself is adapted for piercing skin and sucking blood. Several mouthparts unite to form a needlelike drinking tube. Here's a rundown:

  • Labrum and labium make up the "upper" and "lower" lips
  • Labial palps are long, five-segmented sensory organs that come from the labium.
  • Maxillae is a pair of short, wide plates located in front the labial palps.
  • Maxillary palps: A long, four-segmented palpus comes off each maxilla.
  • Fascicle are three long, slender stylets that are supported within the labial palps.
  • Maxillary lacinae: These are the two outer stylets of the fascicle. They're serrated and blade-like.
  • Median epipharynx: This is the central stylet of the fascicle that joins with the maxillae to form a tube-like food canal.

Fleas use their sharp maxillary laciniae to easily puncture the skin of their host. Then blood travels from their host through the tip of the median epipharynx up the flea's food canal. This requires a lot of suction, which comes from pumps in the flea's mouth and gut.

A flea's legs are adapted for jumping. As with all insects, a flea has three pairs of legs that attach to its thorax. The back legs are very long, and the flea can bend them at several joints. The process of jumping mimics the action of a crossbow. The flea bends its leg, and a pad of elastic protein called resilin stores energy just like a bowstring.

A tendon holds the bent leg in place. When the flea releases this tendon, the leg straightens almost instantly, and the flea accelerates like an arrow from a crossbow. This anatomy gives fleas the ability to jump about 7 inches (17.8 centimeters) vertically or 13 inches (33 centimeters) horizontally. In human proportions, that's a 250-foot (76-meter) vertical jump or a 450-foot (137-meter) horizontal jump. As it lands, the flea uses tiny claws on the ends of its legs to grasp the surface underneath.

Aside from these adaptations, fleas look a lot like most other insects, and their reproductive cycles are similar as well.


Tigers Anatomy

The body of a tiger is built to help them to survive. They are well known for blending into their surroundings, being fast, and being amazing hunters. The body is very muscular and they have a great deal of power behind them. They have large paws with sharp claws and large heads. The whiskers are long and appear on both sides of the face. They typically are going to be longer on the males than on the females.

The colors of the tiger are in place to help them blend into their surroundings with ease. They can have a variety of colors including different shades of brown or orange. They also have areas of white and black that help them to be very distinct. The pattern on any tiger is unique which is part of how they can be identified as individuals.

A tiger actually has two coats of on them. They have guard hair that is long and offers them protection from the elements as well as camouflage. The under fur offers them insulation so that they are able to stay warm enough. They have small ears that are round and they do have good hearing.

Size significantly varies for tigers depending on location and the species. They range from about 100 pounds to over 670 pounds. The males tend to be heavier and taller than the females. Some of the tigers can be close to 12 feet in length. They have very long tails which can account for over 3 feet of that body length.

They only have 30 teeth which is interesting as most carnivores have 42. They back teeth allow them to tear large chunks from their prey. They often swallow that whole instead of taking the time to chew their food. Their digestive system is designed to break down the food. They will gorge themselves when large quantities of food are readily available to them.

Siberian Tiger Close to Water – Tiger Anatomy

There is a gap between their back teeth and that allows them to get deep into the neck of their prey. Then they use their canine teeth to hold it in place until it dies. They have small incisors at the front of the mouth that they use to remove meat from bones and feathers from their prey. The tongue of a tiger has projections that face towards the throat called papillae. They make the tough rough and that helps them to remove fur and feathers from their prey before they consume it.

The back legs of a tiger are longer than those in the front. This is what makes it possible for them to leap up to 32 ½ feet! They have ligaments in the feet that reduce the impact when they run, leap, or pounce. They also have pads on the feet that make it possible for them to move almost silently.

Each claw can be up to 4 inches long. There are 4 claws on each paw and then a dewclaw that is further back. It doesn’t touch the ground when a tiger walks. The dewclaw also helps them to grasp such as how humans use their thumbs. The claws can be retracted when they aren’t needed.

There are some very interesting hybrid tigers out there too worth mentioning. This first took place in the 19 th Century in zoo settings or circus settings for financial gain to attract visitors. The two most common hybrids are known as Ligers and Tigons. This involves lions breeding with tigers. A Liger has a lion father and a mother tiger. A tigon has a tiger father and a lion mother.

There are also some color variations that may occur such as white tigers. This is very rare to occur in the wild but it has been noted to occur. They tend to not live long in the wild as they can’t blend in well to their surroundings. They are also more likely to have birth defects.

Most of the time it is the result of breeding in a zoo setting and these white tigers are very popular with visitors. The problem though is that the white color is the result of a recessive gene which means inbreeding is likely to occur with such practices to produce more of them.

There are also golden tigers that are also the result of a recessive gene. They have a coat that is light gold in color and orange stripes that are very light colored. They also have a coat that is thicker than normal for a tiger. When they are bred in captivity with a White Tiger, they can produce white offspring without any stripes.

Today, practices for hybrids are widely discouraged as they reduce the ability to preserve the various species. However, it is believed such efforts still take place at specialty locations and the zoos in China.


Skeletal System Parts

The anatomy of the skeletal system is complex, and it includes hundreds of bones in the human body. The anatomy of the system varies widely between organisms, as evolution has selected for various adaptations in certain species which change the structure and function of their bones.

Bones serve a variety of functions, but the most important is supporting movement of the limbs and body. Two bones or cartilages are held together at a joint through tough connective tissues called ligaments. Muscles are securely attached to bones through flexible but inelastic connective tissue called tendons. Muscles, joints, tendons, and ligaments are part of the intricate machinery that allows the movement of different bones.

Joints

Functionally, joints can be divided into three classes based on the range of movement they allow in the associated bones. Immovable joints are formed when two bones are held together by fibrous connective tissue with no synovial fluid. These kinds of joints hold the bones of the cranium together.

Partially movable joints are also called cartilaginous joints and are present in the spine and ribs. The third type of joints are called synovial joints and have a fluid-filled synovial cavity that allows the interfacing bones the largest range of movement. Based on the structure of the synovial joints, they can be classified into 6 types, including the hinge joints of the fingers and the ball and socket joints of the hips and shoulders.

Cellular Composition

Each bone is made of complex sets of cells, tissues and a specialized extracellular matrix. The two main cell types are called osteoblasts and osteoclasts with mostly opposing functions. While osteoblasts are involved in the formation of bone, osteoclasts are associated with a reduction in bone mass. The extracellular matrix of the bone consists of collagen and other organic fibers as well as the inorganic component containing calcium salts such as hydroxyapatite. In the interior of bones, a soft tissue called the bone marrow plays an important role in immunity and hematopoiesis. The bone is also richly supplied with nerves and blood vessels.


Where To Shoot A Deer

The definition of what an “ethical shot” is when hunting deer has been an oft debated topic. Whatever your definition may be, a shot that presents the opportunity for the quickest and most humane (and legal) kill should be utilized.

It’s easy for excitement to give way to poor shot selection when hunting (especially when shooting at long range). Unfortunately, this often leads to the wounding of an animal, resulting in unnecessary suffering.

So, where is the kill zone on a deer? The following are locations of a deer’s anatomy, that if properly executed, will result in an effective kill.

Taking into account the position of the deer in this photo, where would you shoot this whitetail? And, which would be the best shot to take?

The Heart Shot

Simply put, a heart shot on a deer is lethal. However, while it will result in the death of a whitetail, it does not necessarily always provide the best blood trails. When the heart is hit, the flow of blood decreases and may result in less of a blood trail than you were hoping for.

bullet or broadhead that penetrates the heart often pierces the lungs as well, which is beneficial to ensuring a quick recovery of the animal.

When taking a heart shot, it’s good to be sure that the caliber of bullet you are using is sufficient to penetrate the shoulder blade and ensure a clean kill. The downside to a larger bullet is it can result in a larger amount of unusable meat upon processing.

The Lung Shot

The lungs provide a large target for rifle hunters and bowhunters alike. While a bullet can enter the lungs of a deer and exit, shooting its lungs with a broadhead will make it difficult for the deer to breathe. Usually, that difficulty breathing will keep it from being able to run too far after the shot. Sometimes, however, simply clipping a lung or not having a complete pass-through shot can result in poor blood trails, making the deer more difficult to track.

A lung shot with a bow is often as effective as a heart shot. Just aim for the middle of the lung area. A well-placed lung shot will cause the deer to suffocate to death. However, a lung-shot attempt that hits too far back may only pierce the liver, which can result in a much slower death and more difficult to track animal.

The Neck Shot

You can drop a deer with one shot if the spinal cord is severed. A neck shot that severs the arteries in the large arteries in the neck can be particularly bloody and lethal. But, while a lethal neck shot causes little damage to the meat of the animal, if the spine is not severed, it could be difficult to recover and it may even survive.

While a neck shot can be a risky shot with a gun, it’s simply a very poor shot to take if you’re a bowhunter.

The angle of the shot should be taken into account when deciding where to shoot a deer.

The Brain Shot

If it is well executed, a brain shot will drop a deer immediately. When you put a bullet through the brain, it will disrupt the life functions of the deer and it will lose consciousness immediately. This shot results in no loss of meat, but is a very difficult shot to make, due to the small target area.

If the shot is not accurate, it can result in unnecessary suffering of the deer and you may not be able to recover the animal.


Cloning and Ethics

Should humans be cloned? Should human cloning be banned? A major objection to human cloning is that cloned embryos are used to produce embryonic stem cells and the cloned embryos are ultimately destroyed. The same objections are raised with regard to stem cell therapy research that uses embryonic stem cells from non-cloned sources. Changing developments in stem cell research, however, could help ease concerns over stem cell use. Scientists have developed new techniques for generating embryonic-like stem cells. These cells could potentially eliminate the need for human embryonic stem cells in therapeutic research. Other ethical concerns about cloning involve the fact that the current process has a very high failure rate. According to the Genetic Science Learning Center, the cloning process only has a success rate of between 0.1 to 3 percent in animals.


Watch the video: Mudvayne perform Dig live at the Oscars 2021 (January 2022).