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Photo shows a crab with orange legs and a black body crawling on a tree.
Muscles attached to the exoskeleton of the Halloween crab ( Gecarcinus quadratus ) allow it to move.


An endoskeleton is a skeleton that consists of hard, mineralized structures located within the soft tissue of organisms. The bones of vertebrates are composed of tissues and mineralized tissues. Endoskeletons provide support for the body, protect internal organs, and allow for movement through contraction of muscles attached to the skeleton.

Photo shows a human skeleton riding a bucking horse skeleton.
The skeletons of humans and horses are examples of endoskeletons. (credit: Ross Murphy)

As an example, the human skeleton is an endoskeleton that consists of 206 bones in the adult. It has five main functions: providing support to the body, storing minerals and lipids, producing blood cells, protecting internal organs, and allowing for movement. The skeletal system in vertebrates is divided into the axial skeleton (which consists of the skull, vertebral column, and rib cage), and the appendicular skeleton (which consists of the shoulders, limb bones, the pectoral girdle, and the pelvic girdle).

Main divisions of the vertebrate skeleton

On a human skeleton, the parts of the axial skeleton are highlighted.
The axial skeleton of humans consists of the bones of the skull, ossicles of the middle ear, hyoid bone, vertebral column, and rib cage. (credit: modification of work by Mariana Ruiz Villareal)
Illustration shows the appendicular skeleton, which consists of arms, legs, shoulder bones, and the pelvic girdle.
The human appendicular skeleton is composed of the bones of the pectoral limbs (arm, forearm, hand), the pelvic limbs (thigh, leg, foot), the pectoral girdle, and the pelvic girdle. (credit: modification of work by Mariana Ruiz Villareal)

Evolution of body design for locomotion on land

The transition of vertebrates from fish ancestors to land-dwelling animals required a number of changes in body design, since movement on land poses challenges that are different from those posed by movement in water. Water provides a certain amount of lift, which is missing on land, so muscles are needed to provide that lift on land. It also provides a medium to push against, and many fish use lateral undulations to push against the water and generate forward movement. Air does not provide the same resistance, and so lateral undulations on land would not produce much movement forward.

As certain fish began to move onto land, they retained their lateral undulation form of locomotion. However, instead of pushing against water, their fins became points of contact with the ground, and the lateral undulations became rotations about those points of contact. The lack of bouyancy provided by water led to increased ossification of the bones and strengthening of the muscles, as well as providing selective pressure that resulted in changes in arrangement of the "wrist" bones of these early tetrapods. The effect of gravity also led to changes in the axial skeleton, since rotations around the contact points with the ground caused new torsional strains on the vertebral column. A firmer, more ossified vertebral column became common in land animals, because it reduces the strain and also provides strength to support the weight of the body. In later tetrapods the vertebrae began allowing for vertical rather than lateral flexing. The vertebrae of the neck also evolved to allow movement of the head independently of the body, a range of motion not found in fish.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Principles of biology. OpenStax CNX. Aug 09, 2016 Download for free at http://legacy.cnx.org/content/col11569/1.25
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