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First of all, let me make it clear that the heart is at the vertical centre of the body -- it is not shifted towards left (or right). However, it is slightly tilted towards the left in most cases.
In some cases, it is tilted towards the right, and the condition is called Dextrocardia. For why it is so, lets look at what the heart does. Below is a diagram ...
answered Jun 14 '17 at 6:57
another 'Homo sapien'
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79
Elephant, rhinoceros, &c all have much thicker legs in proportion. The answer, I think, lies in the fact that the animals you mention all evolved as cursorial animals (that is, they run to escape predators). Less mass in the lower leg means it swings easier, so the animal can run faster.
There are two things you're apparently not noticing in that ...
59
A good exemple should be the “harpoon” in cone snails (Conidae), which is created from a modified tooth inside their proboscis.
(Cone snail with proboscis, from KQED.org)
The harpoon is launched at prey at close distance, and is used to poison and stun prey, and later to pull them in. According to high-speed camera capture the harpoon is launched in just ...
53
This is a mistake in comparative anatomy which is somewhat common. When looking at four-legged animals, people often mistakenly map the parts of the hind legs.
Here is an image that shows the different morphology of the same bones in horses and humans:
What people often think of as the thigh of a four legged creature is really our calf and shin bone! And ...
32
The anus of Octopus is channeled into its siphon.
Image taken from Carina M. Gsottbauer
Note:
Siphon is a tube that leads from the mantle to the outside. Octopuses use their siphon to force water out in jets for propulsion and to flush waste products from the anus.
From Encyclopedia of the Aquatic World, Volume 6
By Marshall Cavendish Corporation
25
According to the highly respected WORMATLAS: A Database of Behavioral and Structural Anatomy of Caenorhabditis elegans, the number is invariable in this animal, one of the most studied in the world.
There are 302 neurons in the nervous system of C. elegans; this number is invariant between animals. Each neuron has a unique combination of properties, such ...
23
It depends what you mean by 'leg'.
The instinctive way to define a 'leg' is based on its functional use: we use legs to walk on. But if we adopt that definition of 'leg' then there certainly are animals with odd numbers of legs: kangaroos, for instance, have a five-legged gait, functionally using their tail as a fifth leg. There is no developmental process ...
23
Your best bet is the Terminologia Anatomica, which is the international standard for anatomical terminology.
The 1998 edition is freely available. It lists only a few named tendons though, which is consistent with my experience as an anatomist: very few tendons are named separately from the muscles to which they are connected. Central tendon of the ...
22
An excellent example (unless you consider this a tool) of a weapon using animal would be the "web casting spiders" which are a diverse group of spiders known as the Deinopidae. These spiders create a special elastic web that they hold between their fore-feet, and then dangling down from a surface, they expand and push the web onto their prey.
There ...
21
How come large herbivores have such thin legs?
They don't. The following book does an extensive comparison of the bones of humans with other animals:
Adams BJ, Crabtree PJ. 2008. Human vs Horse. In: Comparative Skeletal Anatomy. Humana Press.
Here are some images of human bones (left) next to horse bones (right):
Radius/Ulna (fused in horses)
Humerus
...
20
Welcome to Biology.SE!
I think you are talking about plantigrade, digitigrade and unguligrade.
Please note that the number of joints in mammals does NOT vary, but only the relative length (and shape) of the different parts of the leg.
A Plantigrade walks on the sole of the foot. 'Sole' translates to 'planta' in Latin hence the name.
Examples: Human, ...
17
Anatomical terms must be able to fit a wide variety of organisms, from insects to fish, dogs, horses, chimpanzees to humans. That's why the terms are sometimes confusing to people who are thinking only of bipedal humans.
In anatomy, the dorsum is the upper side of animals that typically run fly, swim or crawl in a horizontal position. In vertebrates the ...
17
Short answer
Six legs allow for locomotion, while maintaining a supportive tripod at all times.
Background
There are several million species of insects, all on 6 legs. This implies that any change in this number is promptly selected against. It is generally agreed that insects were derived from many-legged ancestors, e.g. centipedes.
One explanation is ...
17
Although not a hard projectile the Archerfish shoots water
https://en.wikipedia.org/wiki/Archerfish
16
Male mice lack nipples too. Mice are frequently used for embryonic research as they are small and reproduce quickly. It is thought that male mice do develop nipples, but that they regress during development (Wysolmerski, 1998).
In general, it is thought that mammalian organisms develop as females by default when there is no male (Y) chromosome present (...
16
As a couple of counterexamples, species in the classes Symphyla (Pseudocentipedes) and Pauropoda within Myriapoda have 8-11 and 12 leg pairs respectively, so between 16 to 24 legs (sometimes with one or two leg pair stronlgy reduced in size).
(species in Symphyla, from wikipedia)
Another common and species-rich group with 14 walking legs (7 leg pairs) is ...
14
Most mammalian males have nipples. The duck-billed platypus does not have nipples but you begin to see development of nipples in marsupials (Park and Lindberg 2004) like the opossum and kangaroo. Development of a complete nipple begins in the eutherian (placental) mammals.
The mammary glands develop early in the embryo along a pair of ridges called the ...
14
First, for reference, see here for a discussion about the difference in directional terms between bipeds and quadrupeds as well as a fairly complete explanation of word meanings/etymology.
The etymological meanings of the various anatomical directional terms should help explain their usage in body organs. For example:
Ventral -> "belly" side
Dorsal -&...
13
Short answer
The body plan of terrestrial organisms that feature limbs is typically bilaterally symmetric, and hence these organisms have an even number of appendages.
Background
Terrestrial animals featuring appendices for motility (legs, arms) are typically higher organisms. Typically, the body plan of higher animals such as us mammals is typically ...
12
Rotifers are microscopic protostomes with around 1000 cells apiece. This website claims the smallest rotifers have less than 100 cells, but I couldn't confirm this. Most rotifers are eutelic — within a given species, each adult individual has the same number of cells (Encyclopeia of Life: Rotifers).
(Source)
Edit: Myxozoans might be even smaller. These ...
12
The FMA lists 705 tendons, but note that it includes separate terms for left and right instances. As @kmm says, many of these simply shadow the list of skeletal muscles (and is likely incomplete).
You can browse the list on OLS, or if you want to extract a table you can query this SPARQL endpoint, just type in the query here:
SELECT DISTINCT ?x ?v0 WHERE {
...
10
I don't know about all known animals, or actual cell count. However, males of the wasp Dicopomorpha echmepterygis are considered the smallest known insects with a body size of 139 μm. This should at least be a contender for smallest animal. As a reference point, C. elegans are usually about 1mm long.
However, given that we know only about 10% of the ...
10
In general, no.
Car batteries are designed to provide a large amount of amperage, to turn the starter with a high amount of torque via an electric motor. Generally this is done at 12 or 24 volts.
The current recommendations for a defibrillator requires 200V, and a very small amount of amperage. This is one of three settings in a standard defib procedure. ...
10
This depends to some extent on how you define "resting state" (it matters).
Innervation of the eye occurs in the brainstem and upper spinal column, so is, like most brainstem functions, on autopilot (like breathing.)
If you define resting state as that which the lids would assume without any innervation, then the resting state of the eyelids is semi-open. ...
10
Short Answer
This page on wikipedia gives a good synopsis of these concepts.
The confusion lies in the fact that many websites on anatomy discuss/describe/define these terms in relation to humans. However, in quadrupeds and fish (and birds), Anterior/Posterior lies orthogonal to Ventral/Dorsal and are instead synonymous with Cranial(Rostral)/Caudal. ...
10
Many Nematodes do not use traditional hox genes instead the have a strange set up which controls cell placement directly. This means individual adults of many nematode species have the exact same number of cells, it can even be used to identify species. So having the exact same number of neurons is what one should expect in nematodes. https://www.ncbi.nlm....
10
Black herons (Egretta ardesiaca) can overlap their wing tips in front of them while doing what is known as canopy feeding.
9
While it might make more logical sense to have separate passageways for air and food/water, this did not happen in evolutionary history due to the peculiarities of lung development. Vertebrate lungs develop as an outpouching of the gut tube, which itself has a very long evolutionary history (probably homologous among all deuterostomes).
In the image below, ...
9
Males of the carnivorous Jackson's chameleon (Trioceros jacksonii) have three hornlike structures on their heads (also found in a couple of related species). From what I know, these are true horns, which means that they are pointed keratin-covered protrusions that have a core of living bone, see e.g. this website from Toronto Zoo (this page also claims that ...
9
According to textbook of forensic medicine and toxicology by Ks Narayan reddy:
Qualitative differences are:
Male mandible has everted ramus, but female have inverted ramus.
Males have chin U shaped, but it's rounded in females
Quantitative differences:
Suparaorbital ridges are prominent in males but often absent in females.
Mastoid process is wider, ...
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