# Bone growth.



## Anyfoot (Feb 9, 2018)

Hi all. 

I would like to learn more about bone growth. I think it's a vital part of knowing how tortoise grow and in turn could explain more about how we care for them. There's quite a lot on this forum regarding keratin growth. I know @Markw84 , @Tom have helped me in this department a lot, probably more than they realise. But what about bone growth!!!!!! 
Hopefully this discussion will lead to us all being more knowledgeable, I know I have quite a few questions, but as usual questions are dependent on answers to prior questions. 

So my starting questions are:-

Does a tortoise in hibernation or aestivation still gave bone growth, does it still garden off, do fontanelles still fill in during these periods. 

How does existing bone growth. I'm under the impression that new bones in a hatchling are soft cartilage, over time this ossifies into hard bone through absorbing calcium and phosphorus. Is that correct? 
Also what happens to new bone growth, does it always grow as soft cartilage that over time ossifies. This would mean in theory you can have cartilage between hardened(ossified)bone. 

What about when a tortoise us capable of drawing calcium from the bone to lay eggs. How does it replace this calcium? Does bone break down and regenerate? 
If it can does this mean the regeneration of bone can take a different form(shape). If yes then in theory a pyramided tort den smooth off to some extent. 

Does temperature have an effect on bone growth? 

Thanks everyone.


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## Markw84 (Feb 11, 2018)

Anyfoot said:


> Hi all.
> 
> I would like to learn more about bone growth. I think it's a vital part of knowing how tortoise grow and in turn could explain more about how we care for them. There's quite a lot on this forum regarding keratin growth. I know @Markw84 , @Tom have helped me in this department a lot, probably more than they realise. But what about bone growth!!!!!!
> Hopefully this discussion will lead to us all being more knowledgeable, I know I have quite a few questions, but as usual questions are dependent on answers to prior questions.
> ...





Craig;


Sorry for the delay, but I have been out of the loop, forum wise, the past few days with a golf tournament and another social function.

I will share my understanding and current theories of things in relation to your questions and perhaps we can go forward with that. You are asking great questions and from my research, I believe I am at a place no one in chelonian research has ever put together as it comes from so many diverse fields and sources. Yet to me, answers so many questions.

_*"Does a tortoise in hibernation or aestivation still gave bone growth, does it still garden off, do fontanels still fill in during these periods."*_

When a tortoise hibernates/brumates/aestivates it is doing so to shut down most all bodily functions except the minimum required to sustain life. Because conditions are not such that metabolism can function normally - too cold, no UVB, too hot to survive out of cover, no food availability, etc. - Their bodies shut down to extremely low levels. With no new nutrients being added to the system, heart rates and blood flow almost stopped, respiration only high enough to provide minimal oxygen levels - there is nothing being provided for any building blocks for growth. In fact, they would normally be in a deficit mode where the body is using stored reserves just to maintain life. To use those reserves to grow at that time would be counterproductive and dangerous.


*"How does existing bone growth. I'm under the impression that new bones in a hatchling are soft cartilage, over time this ossifies into hard bone through absorbing calcium and phosphorus. Is that correct?"*


Bone growth is quite a conversation in itself. But a basic understanding of how this works I think lends directly to how pyramiding works as I think the direction this discussion will go. It also allows me to combine this with how orthodontics move teeth, so an interesting but related combination.


Bone is in a constant state of building, tearing down and remodeling. During growth years, it is adding mass and becoming more dense at its greatest rate. For humans that period takes about our first 20 years of life and continues at a slower rate for another 10 years or so. A very young tortoise would have more cartilage than "bone". As an embryo develops, it is the cartilage that is formed and shapes what will become bone. A good portion of that then begins to ossify. Calcium and phosphorus is layered on the cartilage cells and as it does, the underlying cartilage cells die off. This creates pockets that begin to develop tiny blood vessels. Now osteoblasts (bone builders) form. They are a basic type of stem cell. Bone marrow is stem cells and creates not only new blood cells constantly for the body, but also other cells like these osteoblasts along with their counterpart - osteoclasts (the bone dissolvers). These new blood vessels allow for these osteoblasts to travel into these newly forming pockets. There they now form collagen fibers and collect calcium to deposit along these fibers. As this continues to encase this osteoblast, the osteoblast then turns into an osteocyte. This is creating a network of open cells of harder calcium phosphate with a softer center. A sponge like yet very strong structure. This allow nutrients, gases and waste to make their way in and out of the bone structure. Bone is living not an inert structural feature alone.


As the osteoblast is doing this, and producing this harder bone structure around itself, eventually it encases itself and gasses that now enter this area along with some osteoclasts that actually starts to decay the osteoblast. They in turn actually take out bone in the center and create room for more marrow. Osteoclasts digest bone with acids and enzymes. So, a network of bone is being built by the osteoblasts and also being digested by the osteoclasts creating the open celled, spongy looking bones with pockets of marrow.


As growth occurs, most of this process continues in zones of the bone towards the ends. In long bones like the forelimbs and legs, this is an area towards the ends but before the joint ends/sockets. But the process is ongoing at slower rates throughout the bone.


SO... if I keep in mind the process of osteoblast building and osteoclast dissolving, I can better understand how those forms of stem cells get called into action throughout the life of the tortoise to constantly build more bone mass, and also to dissolve bone mass to tap into the stores of minerals the bone holds in times of shortage in the bloodstream.


* Also what happens to new bone growth, does it always grow as soft cartilage that over time ossifies. This would mean in theory you can have cartilage between hardened(ossified)bone.*

At a microscopic level, the osteoblasts are creating something similar to cartilage – collagen fibers – in growth areas. They then ossify those fibers. But new larger areas of cartilage are not being created for bone growth. On a cellular level new bone is created by laying down of collagen fiber, mineralization of those fibers encasing the osteoblast, vessels filling in the area, etc, etc. as above. The existing, and more expansive cartilage of the hatchling is constantly being mineralized and converted to bone the first several years, fusing some bone areas and filling in fontanelles. No new cartilage areas are being created.

* 
"What about when a tortoise us capable of drawing calcium from the bone to lay eggs. How does it replace this calcium? Does bone break down and regenerate?"*

The bones are not only structural, but storage areas for vital minerals need to sustain life. In the bones, this is primarily calcium and phosphorus. If blood calcium levels drop and no new calcium is available in the diet, osteoclasts are formed and called into action. They dissolve existing bone. This process releases the mineralized calcium phosphate into the blood as calcium and phosphate ions. Those levels in the bloodstream are necessary for most bodily functions and certainly needed in greater quantities for egg production times. When the diet provides more calcium to the tortoise – building the blood calcium levels to optimum levels, it can again use that calcium to rebuild bone. This is a constant balancing process. Enough calcium available in diet – metabolism and growth of bone mass and density. Calcium deficiency – has to draw from the bones to survive. If that continues – metabolic bone disease and even death.

* "If it can does this mean the regeneration of bone can take a different form(shape).* "

So far, I have discussed how bone grows as a tortoise grows = normal growth. But there is the ongoing process of osteoclasts and osteoblasts being stimulated to form based upon blood calcium levels, (touched on above too) hormone levels, and pressure on the bones themselves.

Bone does not reshape itself. Genetic programming tells it what shape to follow. But bones are constantly remodeling and keeping this cycle going which keeps bone strong. However, external forces do call these processes into play altering the balance. Low blood calcium tells osteoclasts to go out and find bone to convert back to free calcium and phosphorus. Good blood calcium levels tell osteoblasts to build more bone cells and increase the bone mass back. When an animal is young - osteoblasts outnumber osteoclasts and there is more building than dissolving. With exercise, repetitive force on a bone will stimulate more osteoblasts in a bone increases mass and density in the bone. That is why exercise is so key in good bone growth. If a bone is cracked or broken, the osteoblasts are again called into play to fill in the newly forming tissue around the damage with new bone to fill in the gap.

All these processes do not form new shapes. It fills in and strengthens.

*"If yes then in theory a pyramided tort den smooth off to some extent.* "

For my theory on why tortoises pyramided, it became obvious that the scute was the primary force for pyramiding. Drying keratin forced new growth of keratin at the seams downward as it could not spread outward and swell normally top and bottom. So how does this cause the bone to deform?

I was stuck on this and got more and more into bone growth as above. I looked at how keratin grows, as we’ve discussed in other threads. That left me also looking at the epithelial layer – the one thing that separates the two. That lead to some interesting work the past several months.

In vertebrates, epithelial layers are defined by not coming in direct contact with bone areas. They separate wall of organs, the insides of the intestines from the contents of the stomach, the roof of your mouth from the contents of your mouth, etc, etc. everywhere organs come into contact with a different area. But specifically defined as not separating one tissue type from a bone. But in tortoises we have an epithelial layer that separates the bone from the keratin of the scute. In looking at how bone does reshape in every way I could study, I recalled my looking into how orthodontics move teeth. There we have a layer very similar to the epithelial layer in tortoises at the scutes. In our jaws, it is called the periodontal layer. Actually is a type of modified layer that still retains pockets of epithelial cells in pockets throughout the layer. It protects our jawbone from our teeth, providing blood supply etc. to the area and also a bit of a shock absorber for the constant pressure that chewing can exert on the jawbone.

Well guess what they found… If you exert a small but constant pressure on that layer from the tooth, the side that goes into compression triggers the formation of an abundance of osteoclasts (osteoclast genesis) at the point of pressure. Those osteoclasts dissolve bone at that area and relieve that pressure. On the other side of the tooth, the periodontal layer is in tension and the tooth is being pulled away from the bone. That triggers an abundance of osteoblasts to start building extra bone in that area. The bone is not deforming to pressure. The bone is dissolving under pressure and rebuilding in negative pressure on the other side. Your tooth moves and the jaw bone dissolves bone on the pressure side and builds new bone on the other side.

I believe a very similar mechanism is at work with pyramiding. The keratin (we’ve already theorized) was producing pressure downward and compressing the epithelial layer. This would stimulate osteoclast genesis and we would have bone dissolving directly under that pressure area. This creates a groove in the bone under the scute seam as the compression on the epithelial layer is eliminated by the removal of bone under that pressure. With the process repeated with further growth, still in conditions too dry, we have valleys forming. When the dry conditions are corrected, there would no longer be this compression of the epithelial layer and growth would start to smooth out. I would however depend upon how extreme and progressed the previous growth was pyramided, since in a more advance case of pyramiding, the growth of the scute seam is already spreading in an “outward line”. But - that is now tipped in the direction of the previous scute section.

SO – YOUR QUESTION – No. I don’t see how this would then allow the pyramided sections to smooth out and “correct”. Bone (osteoclast genesis) is only reacting to pressure on the epithelial layer – (periodontal layer in jaws) for this process. No pressure is being exerted with an established part of a scute that would compress the epithelial layer and trigger osteoclast genesis.

* "Does temperature have an effect on bone growth?"*

Yes. Since tortoises are ectotherms. - Temperature dictates metabolic activity. Bone growth is an expensive metabolic process. If not given optimal conditions, all of this would be severely impacted.


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## Anyfoot (Feb 11, 2018)

Well Mark, I'm more than impressed. I have questions but it will have to wait until tomorrow because it's late here. I must start proof reading my posts, my fat fingers and this iPhone don't mix. Apologies for my errors. 

One quick question to be going on with for now. 
Does the ossification of the original cartilage in a hatchling happen evenly all over or does it start from a specific point(areola maybe) and work out. 
My babies at about 6 months old look like they are getting raised scutes but at 12/18 months old do look to be smoothing back off. Maybe this is ossification in progress or maybe it's the overall shape and size of the tort developing that makes it smooth off.


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## Anyfoot (Feb 12, 2018)

I'm trying to work out if it's possible that we can grow a tortoise too fast in the first few mths/yrs because we've grown it without bone ossification coming first. 
But if a combination of osteoblasts and osteoclasts are breaking down and rebuilding bone structure then the actual ossification is running on par with the tortoise growing anyway. In theory if tortoise 'A' grows twice as fast as tortoise 'B' then tortoise 'A' has also ossified twice as fast. Is that correct? 
Or is it possible to acquire an abundance of calcium,phosphorus,minerals and not proteins so ossification happens faster than growth. 
Can minerals and vitamins be absorbed through the skin to aid bone ossification? So for example a hatchling is dug in a calcium rich soil, does it benefit from this? This would in theory fall in line with a med species neonate hibernating through colder times or a radiated neonate aestivating through the hot dry arid times. 

I've got a thought that if we got a hatchlings cartilages to ossify more before growth commenced then the hardened bone would be forced to grow more in the correct direction than cartilage would. Surely hard keratin can push cartilage down easier than hardened bone. If yes then the best combination would be hardened bone and soft supple keratin to get the correct bone growth direction(across).


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## Markw84 (Feb 12, 2018)

Anyfoot said:


> I'm trying to work out if it's possible that we can grow a tortoise too fast in the first few mths/yrs because we've grown it without bone ossification coming first.
> But if a combination of osteoblasts and osteoclasts are breaking down and rebuilding bone structure then the actual ossification is running on par with the tortoise growing anyway. In theory if tortoise 'A' grows twice as fast as tortoise 'B' then tortoise 'A' has also ossified twice as fast. Is that correct?
> Or is it possible to acquire an abundance of calcium,phosphorus,minerals and not proteins so ossification happens faster than growth.
> Can minerals and vitamins be absorbed through the skin to aid bone ossification? So for example a hatchling is dug in a calcium rich soil, does it benefit from this? This would in theory fall in line with a med species neonate hibernating through colder times or a radiated neonate aestivating through the hot dry arid times.
> ...



Perhaps there is confusion by the loose use of ossification. There are actually two types. One is where existing cartilage is replaced by bone. Endochondral Ossification. The other is more the remodeling process where ossification occurs within a membrane. Intramembranous Ossification. That is involved in building bone mass, growing bone, repairing fractures, etc, etc. However, I think it will help if we think of all the bone processes as two separate things: 1 - normal growth. 2 - Metabolic adjusting to compensate for living conditions.

NORMAL GROWTH = When a tortoise hatches, most all the bone is already ossified. As an embryo develops, cartilage is first shaped where the bones will be. As embryonic development continues, that cartilage is mineralized and turned to bone. This is Endochondral Ossification. This Ossification is a process of embryo development just as developing nails on the feet, or scales on the skin. Even in humans, the ossification of bone is almost complete upon birth, however there is a fontanel in the head - (soft spot) that takes a bit longer. In tortoises, with the adapted rib structure, there are fontanels left separating the lower half of the ribs as they extend down. So this filling in of fontanel is an extension of the embryonic development to "turn into a tortoise". It simply takes longer and extends out a few years for those bones to totally fill in and close the entire shell structure. This process would be making the fontanel smaller and smaller as it fills in. So it is growth that is radiating outward with the rib bones growing towards each other. This process is genetically programmed and timed. A bigger tortoise would not fill in faster than a smaller tortoise. It is a programmed, timed development process that simply extends beyond the egg. Natural growth which includes bone growing and strengthening is also part of that process. In humans that lasts 20 years then slows and goes on another 10 years. Then, the human is DONE! For a tortoise growth can vary depending upon the ability to find conditions that allow growth to continue. Humans do not have that programming. When conditions are good, a tortoise will grow quite quickly to reach a more "predator proof" size and breeding size as quickly as possible. But the sequence of growing is set. One leg will not grow faster than another. The head will not grow faster than the rear foot. One part cannot "outgrow" another part.

METABOLIC ADJUSTMENTS = Pyramiding, MBD, dissolving bone to replenish low blood calcium/poor diet, are different things. These are not "programmed sequenced" events. They are reactions to what the tortoise is being subjected to. In good conditions, they may never happen. In laying eggs, it happens only in response to the formation of eggs if coupled with low diet calcium levels.

*Does the ossification of the original cartilage in a hatchling happen evenly all over or does it start from a specific point(areola maybe) and work out.
*
This is part of normal growth. Keep in mind most all bone is already calcified bone upon hatching, The scute areolae seem to be "attached" at areas that have bone beneath. Notice how the costal areolae are at the upper ends of the costals where the ribs have already met and there are no fontanels there. So the only fontanels filling in are at the lower half of the ribs. This is filling in the fontanel that is between the lower part of the ribs and the peripheral bones. This would be happening from the edges in. The rest of the skeleton is already formed. It will grow, but it is already formed.

The only area we are dealing with the normal growth of cartilage being ossified once a tortoise hatches is these fontanels. The rest of the skeleton is bone. Here is a 1 yr old sulcata skeleton on top of a 2 year old. You can see how the fontanels are filling in. You can imagine where the costal areolae would lie towards the top of the scute where there is bone already formed in the youngest sulcata.




*In theory if tortoise 'A' grows twice as fast as tortoise 'B' then tortoise 'A' has also ossified twice as fast. Is that correct?*

Possibly. But "ossification" here is referring to filing in fontanels. Replacing the little remaining cartilage that initially formed the skeletal structure with bone to complete the skeleton. Just like a baby human filling in - ossifying - the soft spot. That is a process of maturing. A genetically sequenced event. But in a tortoise, this is also probably similar to sexual maturity. In tortoises these things are indeed greatly impacted by how much optimal conditions are available to allow faster growth. The entire tortoise is maturing faster with faster/more growth. The larger tortoise would be closer to sexual maturity, and I would assume the filling in of the fontanels has matured further along with the faster growth as well.

*Or is it possible to acquire an abundance of calcium,phosphorus,minerals and not proteins so ossification happens faster than growth*

Optimal levels allow fast growth with proper hydration and temperatures. A lack of essential minerals in the blood would stop growth, and lead to death. Excess minerals would be processed by kidney and liver and excreted out. A lack of protein would stop growth and lead to death. You cannot have growth without proteins. You could have growth with an imbalance of some minerals. With calcium = MBD.

The ossification of cartilage is only happening at the fontanels in a young tortoise. Very early in the development of an embryo - all the cartilage areas that will become bone are already formed. The intramembranous ossification is constantly happening with a growing tortoise - adding size and density, replacing old bone, etc. That very process requires protein. The first stages is the osteoblast creating collagen fibers. That in turn is mineralized and is the base for where the new bone will be. This is at a cellular level. This is not like a whole new area of cartilage forming that will later be ossified.

*Can minerals and vitamins be absorbed through the skin to aid bone ossification? So for example a hatchling is dug in a calcium rich soil, does it benefit from this? This would in theory fall in line with a med species neonate hibernating through colder times or a radiated neonate aestivating through the hot dry arid times*.

A tortoise is not absorbing minerals through the skin. Calcium, phosphorus and other minerals are through digestion, broken into ionic calcium and organic phosphates. These present in the blood are what the body works with. While still in the egg, however, available calcium ions are absorbed through the eggshell and can add to the calcium uptake of the embryo. Other chemicals that come into contact with the eggshell can also interfere and block calcium uptake. However this is happening through the connection to the yolk. Once hatched, it is ingested minerals that are needed.

*I've got a thought that if we got a hatchlings cartilages to ossify more before growth commenced then the hardened bone would be forced to grow more in the correct direction than cartilage would. Surely hard keratin can push cartilage down easier than hardened bone. If yes then the best combination would be hardened bone and soft supple keratin to get the correct bone growth direction(across).*

But we do have hardened bone where you see pyramiding. The scutes that pyramid are above bone already formed. The only cartilage (fontanels) in a tortoise are in the lower costals. AND... according to my theory, it is hardened bone that pyramids! Bone reacts to a slight but constant pressure which puts the epithelial layer in compression. That triggers osteoclasts to do their work and remove bone to release that pressure. That does not happen with cartilage. The BONE is remodeling and forming the valleys you see as pyramiding. So, yes, soft supple new keratin is the answer to prevent pyramiding. That means new growth must be without excessively dry conditions. Because that causes the keratin at the new scute edges to harden on top where exposed and force the growth and swelling of the new keratin seam downward. Compressing the epithelial layer...


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## Anyfoot (Feb 13, 2018)

It's all making sense and sounds logical up to now Mark.

Is it possible to tip the bone angle by growing a tortoise in lower temps than it's used to. When I watch my torts grow I dread seeing a crevice between scutes. What I want to see is thin white lines of keratin following steady growth.
I'm thinking these crevices I'm seeing could coincide with the lower temps in my tort house through a couple months of winter. So normally I'm at around 27deg c, During Dec/Jan when it get to -5deg c outside my tort house does drop to 23/24deg c. Could this create a tipping of bone? Maybe new keratin is more brittle at lower temps and is acting the same as if it wasn't kept moist and supple.


This question is not on bone but it's related to what we are talking about I think.

When we soak our babies why does this contribute to keeping the top outside keratin layer supple. Are we assuming that everyone splashes the carapace to keep it supple on the external side?


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## Markw84 (Feb 13, 2018)

I don't think we have an answer to that question. I tend to think it is more related to stress and change when I see a bigger ridge developing. In my research on bone growth, I see lots of research on how stress inhibits blood mineral levels and suppresses the formation of osteoblasts ( the builders, but not the dissolvers).

Cooler temps could be playing a role. Cooler temps reduces blood flow and certainly that could extend to blood flow though the epithelial layer. So with good daytime conditions still in the high growth mode, an excessive night drop (or any drop) could possibly reduce (or delay) new keratin production at the growing seam. In their natural environment, the tortoises we associate with a propensity to pyramid all come from areas where in their growing season, the nighttime temps do not drop much below 80°f. OR, in the case of radiata and elegans, the average daily temp is still at or above 80° so hiding in cover for the night, they can still maintain 80° body temps.
Sulcatas - average nighttime low Mar - Jun is at or above 80°
Radiata - average low Nov - Apr is at or above 74°
Platynota - average low Apr - Oct is at or above 80°
Elegans - average low Apr - Oct at or above 70°
Carbonaria - average low (Columbia range) never gets below 81°

Soaking? Not sure on that. When I soak my tortoises, I frequently run water over the shell and try to keep the carapace as wet as possible. For a real effort to keep a "perfect" as possible, I also mist/spray them down whenever I get a chance. Everything to keep the carapace wetter. My hunch would be that you could grow a pretty smooth tortoise will simply good high humidity, and no forced soaks. Good experiment??

Perhaps @Tom has done some experiments with high humidity and not soaking / daily soaking and lower humidity. Certainly for overall metabolic hydration, and for exercise, the soaking is so beneficial. For keratin growth on the carapace, I believe it would also certainly be of benefit to have that added hydration as new keratin is very hydroscopic and that once a day re-absorption of good moisture would add to the overall state of the keratin throughout the day. My belief is that high humidity will play the biggest role pyramiding wise.


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## Anyfoot (Feb 13, 2018)

I spray every morning, I've soaked every baby every day for the first 3 to 6 months. Now I soak every other day, and I have a clutch of 10 that are soaked ever 3rd day from 3 months old. 
I'm now adding nutrobal at least 3 times a wk to all my babies(since I got radiated) and I'm seeing the thin white lines a lot more. 

I'm coming to the conclusion anything below 99% humidity is not going to give a constant smooth reading over a large number of torts, some will be smooth at 80% and some not so smooth, I'm guessing this is because of individual habits. 
Thinking back my 3 smooth juveniles were in a viv that was almost always 99%. They also dug into moist deep coir, no wood chips to impede digging and I only soaked 3 times a wk. Trouble is back then I wasn't as obsessed and as wise as I am now so some things will have gone unnoticed to my untrained eye. 
I also fed those 3 anything and everything at some stage.


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## Anyfoot (Feb 16, 2018)

Have you ever seen a well established tortoise(let's say 2yrs and older) start to pyramiding after a good smooth start in life? ANYONE.


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## Anyfoot (Feb 16, 2018)

@Markw84 
What's the chances of you putting a thread together with details on keratin and bone growth and how it all relates to pyramiding and how we should care for every species in the earlier stages of life. 
So I can start to link it onto FB groups. I need one post I can link in, not 3 or 4 that we've all discussed in over past months. 

I know I'm asking for a lot of work and it will take time, and it will be you repeating yourself. But as it is at the moment for a reader to connect bone and keratin growth together they have to read at least 2 or 3 different threads.


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