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Post by aimee benitez on March 1, 2014

this lectures have been really helpful for me. im studying for the dental board part 1 (NBDE1)and this lectures are perfect because they cover pretty much everything we learned at dental school or pre med so its kind of a refreshing for all those concepts and knowledge from our student years!! great ! thanks a lot!!

Axial Skeleton

  • The axial skeleton includes the skull, hyoid, vertebrae, and the thoracic (rib) cage
  • The skull has 22 bones and includes the frontal, parietal, temporal, occipital, sphenoid, and ethmoid bones
  • The skull bones can be divided into cranial bones and facial bones
  • The hyoid bone is located in the neck region and helps attach muscles associated with the tongue and helps with swallowing
  • The vertebral column contains 26 bones and is divided into cervical, thoracic, lumbar, and pelvic curvatures
  • The thoracic cage contains 12 pairs of ribs and the sternum
  • Did you know…
    • Q: Why aren’t teeth mentioned in the axial skeleton lesson?
    • A: Technically teeth are not bones. They are in the jaws of the skull (in the maxillae and mandible) but anatomically their contents differ from actual bone and they are not included in the list of 206 bones of the adult human body. They are discussed in the digestive system lesson.

Axial Skeleton

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Axial Skeleton 0:05
    • Skull
    • Hyoid
    • Vertebral Column
    • Thoracic Cage
  • Skull 0:35
    • Cranium
    • Sphenoid
    • Ethmoid
  • Frontal Bone 1:32
    • Sinuses
    • Sutures
  • Parietal Bones 3:29
    • Sutures
    • Most Superior / Lateral Cranial Bones
    • Fontanelles
  • Temporal Bones 5:00
    • Zygomatic Process
    • External Auditory Meatus
    • Mastoid Process
    • Styloid Process
    • Mandibular Fossa
    • Carotid Canals
  • Occipital Bone 8:12
    • Foramen Magnum
    • Occipital Condyle
    • Jugular Foramina
  • Sphenoid Bone 10:11
    • Forms Part of the Inferior Portion of the Cranium
    • Connects Cranium to Facial Bones
    • Has a Pair of Sinuses
    • Sella Turcica
    • Optic Canals
    • Greater/ Lesser Wings
  • Superior View of Cranium Interior 12:33
  • Ethmoid Bone 13:09
    • Forms the Superior Portion of Nasal Cavity
    • Images Contain the Crista Galli, Nasal Conchae, Perpendicular Plate, and 2 Sinuses
  • Maxillae 15:29
    • Holds the Upper Teeth, Forms the Inferior Portion of the Orbit, and Make Up the Upper Jaw and Hard Palate
  • Palatine Bones 16:17
  • Nasal Cavity Bones 16:55
    • Nasal Bones
    • Vomer
    • Interior Nasal Conchae
  • Sagittal Cross Section Through the Skull 19:03
  • More Facial Bones 19:45
    • Zygomatic Bones
    • Lacrimal Bones
  • Mandible 20:58
    • Lower Jaw Bone
    • Mandibular Condyles
  • Hyoid Bone 21:39
    • Supports the Larynx
    • Does Not Articular with Any Other Bones
  • Vertebral Column 22:45
    • 26 Bones
    • There Are Cartilage Pads Called 'Intervertebral Discs' Between Each Vertebra
  • Vertebral Curvatures 24:55
    • Cervical
    • Thoracic
    • Lumbar
    • Atlas
    • Axis
    • Pelvic
  • Vertebral Column Side View 28:33
  • Sacrum/ Coccyx 29:29
    • Sacrum Has 5 Pieces
    • Coccyx Usually Has 4 Pieces
  • Thoracic Cage 31:00
    • 12 Pairs of Ribs
    • Sternum
    • Costal Cartilage

Transcription: Axial Skeleton

Hi and welcome back to www.educator.com0000

This is the lesson on axial skeleton.0002

The axial skeleton is the part of the skeleton that is along to your axis down the middle.0004

This is the middle of the body so every bone in this section is considered part of it.0015

That includes the skull, hyoid bone, vertebral column, and the thoracic cage.0021

Let us start with the skull at the most superior portion of the axial skeleton.0033

The cranium is all of this business right here.0041

That includes the frontal bone, parietal bone, temporal bone, occipital bone.0047

You can see we have a sagittal cross section straight to the skull here.0053

There are 2 other bones that are associated with the cranium, the sphenoid and the ethmoid bone which makes up a lot of the nasal cavity.0057

They do articulate with those of the cranial bones.0081

They form at least a part of the cranial cavity so they are considered part of the cranium as well.0085

The frontal bone includes 2 major parts.0091

The sinuses are hollow cavities within bone.0098

The 2 frontal sinuses are approximately here and they serve a couple of purposes.0104

One of them is these hollow portions within the bone make the bone weigh less.0112

It has less mass.0118

If all of the sinuses the 8 cavities within our skull were filled with bones our skull will be a little heavier.0120

If that was the case maybe we will get used to it.0127

Having that slightly hollow area does reduce the weight of the bone.0129

Within those cavities have mucous membranes that create secretions for the sake of catching bacteria before they spread deeper in to more vulnerable organs in the body.0134

Some of the cavities or sinuses in the skull section they do connect to the nasal cavity in terms of producing mucous and helping clean out that area.0149

If you get a headache it could be because you have a swelling within the sinuses of your frontal bone.0161

Sutures are those immovable joints that connect a bone to another bone.0169

You have suture that connect the frontal bone and the parietal bone on the side.0179

You have sutures right here that connect the frontal bone to the maxillae.0185

Part of the frontal bone does form part of the orbit of the eye.0194

The orbit of the eye would be the giant eye holes that you see in the skull.0201

That is the frontal bone.0205

Next up is the parietal bone and you could see there is a major suture right here and this is called the sagittal suture but that connects the 2 parietal bone to each other.0208

You could see that there is a suture right here connecting it to the frontal bone.0225

The 2 parietal bones together are the most superior and lateral cranial bones in the entire skull.0229

Because they are here on the top and you can see little bulges on the side.0235

This part of the skull is the most to the side of any part of the head.0239

You can see that I did not list sinuses here.0246

They are not any major sinuses in the parietal bones.0250

Something else is of interest is the fontanelles.0252

The word fontanelle is associated with infants, those soft spots of the baby’s head that you must be careful with.0256

When a baby comes out you want the skull to be slightly flexible so that they can get to the birth canal properly 0267

and also to allow for lots of brain growth that happens in the first several years of life.0274

In my skull there are no more fontanelles.0280

Those soft spots are filled with hard bones and immovable sutures.0282

Those fontanelles in a baby’s skull are soft spots you are going to see where the sutures will be when they are full grown.0288

The temporal bones next to the temples of your head.0299

There are several interesting things coming out of the temporal bones that are very important with shape that I want to cover with you.0304

The zygomatic process that is right here.0313

That does connect to the zygomatic bone.0317

This is not part of the temporal bone.0321

This check bone is called the zygomaticus but if you follow it back here, this is the most anterior part 0322

of the temporal bone and there is an immovable suture to the cheek bone.0336

The external auditory meatus also called the external acoustic meatus is your ear hole.0341

Here it is.0348

You got the actual auricle or pinna of the ear here but the hole is in the bone as well and that is leading to the inner ear.0350

The mastoid process is this little bulge here and you can barely feel it.0364

If you go behind the ear, there is a little bump that comes right next to the lobe.0375

You have a lot of attachment on the neck muscles there which is very important for moving your head around.0382

Next up is the styloid process.0388

A lot of skulls I have seen that part will easily break off if people are not careful.0393

I had skulls in classrooms before where there are no more styloid process.0403

I cannot have you feel it because it is too deep.0407

You cannot possibly feel it, do not try.0413

You have that connected to the parts of your throat and your tongue.0415

That is the reason why you cannot touch it.0420

The mandibular fossa.0423

Fossa is a term for anytime you have a well that something else fits into.0426

This is the mandible which we will cover towards the end of this lesson. 0434

The tops of this bone fit in nicely to a part of the temporal bone.0437

It is hard for me to label it there because it is tucked underneath but next to the mastoid processes you have these mandibular fossae.0443

Fossae would be plural.0452

You have these little condyles, these little bony projections of the jaw bone fitting nicely in there.0454

Those are the mandibular fossae on either side of the skull because you have 2 temporal bones.0463

One of the other ones that I want to mention is the carotid canals.0469

The carotid canals are hard to see in this particular image but the carotid arteries that feed your brain 0474

with blood every second of the day go through the temporal bones to get up to the brain.0484

The occipital bone, if you flip a skull up you have to look at the bottom to see it but it is also at the back.0490

The occipital bone does come up here but the majority of it is tucked under.0504

This giant hole here is called the foramen magnum.0510

Magnum meaning large and foramen is a fancy anatomical word for a whole in a bone.0516

Plural word is foramina, you do not use the word foramen that does exist but if you want to talk about numerous of these things the term is foramina.0523

You just have one giant hole there and you can probably guess what comes out of it.0532

The brain stem leading to the spinal cord comes trough that particular passageway.0537

The occipital condyle.0542

On the occipital bone you do have these 2 parts that jagged out next to the foramen magnum 0545

and the first vertebra or the top bone of your vertebral column fits nicely with those condyles.0559

It is called the atlas and it fits perfectly to the occipital condyles.0567

Lastly is the jugular foramina.0573

It is tough to see here in this particular image but the jugular foramina are 2 holes that the jugular veins come out of.0577

The carotid arteries those feed the brain with the blood and the veins that come out of your cranial cavity, 0586

the jugular foramina hold the jugular veins coming out and going down the neck and connecting back to the heart through the vena cava.0597

The sphenoid we are towards the end of the cranial section of this presentation.0609

I like to nick name this the bat bone.0618

It looks like a bat to me.0620

If you look at this image we are looking straight through the back of the skull.0627

You can see that it kind of have this wing like a bat.0633

The foremost part of the inferior portion of the cranium, that sagittal cross section we saw it was towards the anterior portion of the cranial cavity.0637

It connects the cranium to the facial bones. 0650

A lot of facial bones that we will cover a little bit later on this lesson articulate with the sphenoid. 0653

Straight back through the eyes and nasal region that is where the sphenoid bone is located.0657

There is a pair of sinuses in here too.0666

These sinuses produce mucous that helps strain into the nasal cavity to clear out some of the bacteria and viruses that you can inhale through that region.0668

More on the sphenoid bone.0678

The sella turcica is a little well and there is another image we saw earlier where the sphenoid from the side look like it had this little well.0683

Almost like a saddle and sella turcica means Turkish saddle.0699

If you are wondering what is the cowboy riding in that saddle, it is the pituitary gland.0706

That is where the pituitary gland is found.0710

If we cut this in half you will be able to see that.0715

There is an image later on the lesson where it is visible.0718

The optic canals are for the optic nerves.0721

The sphenoid is behind the eyes, the optic nerves that come from the posterior portion of the eyes 0726

they go to the optic canals on the way to the back of the brain on the occipital lobe.0732

Greater and lesser wings, the greater wings are these big ones here and the lesser wings are these tinier little extensions.0737

Here is s superior view of the cranium anterior.0751

If you remove the parietal bones and keep the rest you can see how it all fits in.0758

The one we have not covered is the ethmoid bone but it is coming up in a bit.0766

You can see those wings of the sphenoid, the lesser wings here.0769

You can see all the temporal bones on either side fit in or articulate with that sphenoidal bone.0775

The frontal bone has it own sutures connecting to it as well.0783

What is this ethomid bone?0787

This is the final part that articulates with the cranium.0791

It forms the superior portion or upper part of that nasal cavity and part of the septum.0795

The septum we often to refer as the skin/cartilage portion of the septum.0802

But if you go back further there is a bony septum, a bony separation between the 2 sides of the nasal cavity.0809

It is also part of the cranial floor.0817

In that previous image remember seeing the ethmoid made up a part of that anterior of the cranium.0820

Ever so slightly part of the orbit of the eye is thanks to the sides of the ethmoid.0826

Here are 2 images from Gray’s Anatomy. This particular one we are looking posteriorly at this particular ethmoid bone.0833

It contains what is called the crista galli.0843

What is this crista galli?0846

Crista galli stands for cocci cone, like that part on the rooster, that very typical red hanging thing on a rooster’s head.0848

Someone who is looking at this named the little part of the ethomid that is protruding up to the cranial cavity the crista galli.0859

If you use your imagination it is remindful of that lilt think poking out.0869

It barely protrudes in the cranial cavity.0874

The nasal conchae this section all in here are nasal conchae.0878

Conch, like that particular spiral shell, is this twisting making up those nasal cavity bones.0887

The perpendicular plate is in the very middle of the ethmoid protruding down this is that bony septum, the majority of it.0902

It is straight back through here.0914

There are also 2 ethmoid sinuses, 2 cavities within this bone that help drain out that nasal cavity.0917

We are moving to the facial bones.0927

The maxillae are 2 bones and each one is called a maxilla.0932

Here is a suture right here.0936

You can see that this is a very peculiar shape compared to the other bones.0938

Each one is a maxilla.0945

You can see that they hold the upper teeth, form the inferior portion of the orbit here and make up the upper jaw and hard palate.0948

There is a soft palate that is more posterior further back.0960

We will get to that later.0965

The last set of sinuses is located in the maxillae.0966

That is a total of 8 sinuses in the skull for 4 pairs.0971

The palatine bones those do connect with the parts of the nasal cavity.0975

It is like a golf post.0982

You can see that shape here from this particular view those 2 bones that fit in.0984

You got the parts that are lateral that hugs the ethmoid bone and connected to the maxillae which we just covered, 0991

posterior to the maxilla, hard palate portion, you got the palatine making up a part of the hard palate that is further back.1002

Nasal cavity bones are some more bones associated with all that twisting turning stuff behind the fleshy cartilage nose.1012

The nasal bones if you notice the bridge of the nose right up here is very hard.1025

All of these in here are skin and cartilage but right here, which has a lot to do with the shape of your nose are 2 nasal bones.1032

When someone breaks their nose, chances are they are breaking their nasal bones possibly parts of the ethmoid deeper.1040

The only bones in the proper nose are right here and there are 2 of them.1047

Because of the sagittal cross section we are only seeing one but here is one of those nasal bones and you could see it articulates with the frontal bone.1054

The vomer which we are going to see a little bit more clearly in a future image here is right beneath the ethmoid 1062

and forms the most inferior part of that bony septum but it is connected to the maxillae but is further back.1071

Finally the inferior nasal conchae, each one is a concha.1080

If we look at the ethmoid bone as being that twisty turning bone with the perpendicular plate in the middle, 1085

here is that crista galli, if you touch the side it is kind of the E.1098

That is how I remember that is the ethmoid because the ethmoid looks like an E tilted.1103

The inferior nasal conchae are these little units coming off the most inferior part of the ethmoid bone.1108

The very tiny bones they call them the inferior nasal conchae because they are on the bottom part of it.1121

This one here is the sella turcica. 1126

You can see from this image a very clear view of that saddle where you would find the pituitary gland.1130

There is the sphenoidal sinus.1138

Here is another great view of sagittal section where we can look at the bones that we have looked over.1141

You can see the temporal bone from inside of the cranial cavity.1148

Here is the sphenoid bone once again, sella turcica with the sinus.1152

There is that vomer bone and like I said it articulates with the maxillae and the ethmoid bone and when you have that perfect cross section you can see the vomer.1159

The previous slide was probably a sagittal cross section slightly to the side or slightly lateral.1169

When it is perfectly medial like this you would be cutting right where the vomer bone is.1177

A couple more of facial bones.1182

When we look at the section of the skull there is the maxilla.1188

Here is that cheek bone, the zygomatic bone.1191

It does articulate with the zygomatic process of the temporal bone.1196

Those check bones have a lot to do with the shape of your face as well as the other skull bones and they are called the zygomatic bones.1200

It is a muscle called the zygomaticus it attaches right there.1207

The lacrimal bones they are not labeled in this drawing but I will show you where they are.1211

Lacrimal comes from the Spanish word lagrima which means tear.1216

It comes from the same Latin root.1223

They are tucked into the sides here and you cannot touch them because they are on the sides of your eye balls.1225

They have that name because they help drain tears from the eye area down in to the nasal cavity.1234

This does connect into the nasal conchae through a little passageway there.1241

It is brilliant how it works.1245

Some tear do emerge out of the eye to the cheek but other tears can drain into that lacrimal bone passageway.1248

The mandible or lower jaw bone.1256

It contains the lower teeth.1261

The mandibular condyles are right here.1263

Those do connect with the mandibular fosae1269

This particular process attaches to muscles that help with the particular movement your jaw makes whether you are talking, chewing.1276

If you do look at the mandibular fosae it is a perfect fit for the mandibular condyles.1290

One of the bones of the axial skeleton that is often forgotten is the hyoid bone.1296

If you come up on your throat you can feel a very hard bony section above your larynx.1306

Here is the Adam’s apple larynx section but the hyoid bone is just above it and you can see that.1315

Here is that typical Adam’s apple looking thing which we will cover later in the respiratory system chapter.1321

This is the hyoid bone.1330

This is one of those unique bones in the human body that does not touch other any bones.1332

That is rare.1339

Figure out any bone in your body it is articulating or making a joint with something else.1340

This is connected to other bones via ligaments but it is free floating.1344

It helps with talking, swallowing, your tongue is attached to it.1351

It is a very important bone but not touching any other bone.1359

The vertebral column also known as the spine.1363

There are 26 total bones in the human body.1368

24 of them are typical vertebrae.1371

A vertebra is singular.1374

At the bottom you have the sacrum and coccyx.1377

There are cartilaginous pads called inter vertebral disks between each of the vertebrae.1380

We will see that better in future images.1387

Those little pads are not only for cushioning but it is how these bones are articulating with respect to one another.1390

Every movement you make with your back they are ever so slight movement of those bones with those cartilaginous pads.1399

You could see these are major portions here, anatomical sections that are important to remember.1409

The body of each one of these vertebrae is where that cartilaginous pad is.1416

There is one on the top and one on the bottom to help fit into the other ones above it and below it.1423

Vertebral foramen as you can guess, the spinal cord fits into the vertebral foramina.1428

The spinous process which is the most posterior part, the body will be the most anterior part.1439

The spinous process most posterior or dorsal is when someone bends over and you se those back bones you are looking at the spinous processes.1449

Sometimes they protrude more on other people than others but they attach a lot of back muscles.1458

The transverse process is the last one I am going to mention.1465

The transverse process they say transverse because they come out horizontally.1469

That is where you have the back of the ribs fitting into each of those back bones or vertebrae.1474

There is a little well or a fosae that fits very well with a little condyle, a little protruding part on the ribs.1481

When we look into the vertebral curvature there are 4 major ones.1493

There is the cervical meaning neck, the thoracic which has to do with the thoracic cage, the lumbar or lower back, pelvic curvature also known as the tail bone.1499

There are 2 bones I wanted to show you from the cervical vertebrae and you have 7 neck vertebrae.1510

You have to say c1 to c7 and once you get to t1 that is where the first rib is that is why they have that separation. 1517

I want to show you atlas and axis.1525

Atlas is also known as c1 and this is also known as c2.1527

The top 2 are most superior part of the cervical vertebrae1535

The atlas is named after that mythological figure Atlas, who you can see in images holding the entire world.1541

This is a clever name for c1 because the atlas vertebra is right under your skull and that is connected to the occipital bone.1549

I told you that there are those parts on the occipital bone that articulate with the first vertebra.1558

They articulate with these 2 things here called the superior articular facets.1565

It is a clever name because that bone is holding up your world which is all in your head.1570

Right beneath that fitting into part of this little foramen you do have the axis.1577

That is a great name because the axis rotates so that your head can move back and forth.1587

The atlas will remain still against your skull but your axis is rotating around.1594

When we look at the other sections the thoracic lumbar.1603

This is a typical thoracic vertebra this is where you are going to have significant transverse processes because you have to have ribs attached to it.1608

You do have 12 pairs of ribs so there are 12 thoracic vertebrae.1618

You got this hole where your spinal cord is going through it.1626

When you compare the size of the hole here to the size of the average cervical vertebra they can get a little bit smaller.1632

As your spinal cord goes down your back and you have nerves extending off of it, it is like taking traffic away from what is farther down or more inferior.1641

The spinal cord gets slightly thinner when as go down.1653

When you get to the lumbar vertebra at the very bottom proportionally it looks like smaller hole compared to those bones.1658

It makes sense that the body changes size.1668

Look at the body on the cervical vertebrae not nearly as much, there is slightly less weight to hold up there.1671

As you are further down the vertebral column, more and more weight is being held there so 1679

you are going to see the body size significantly larger on the lumbar vertebrae.1686

There are 5 lumbar vertebrae and they are quite large compared to the ones superior to it.1692

The pelvic curvature is that part of the tail bone at the bottom that is right in between of the pelvis bones which we will cover more in the appendicular skeleton. 1698

Here is that vertebral column side view you can see the 7 cervical, 12 thoracic, 5 lumbar, and here is that pelvic curvature made up of 2 major bones.1711

The back bone when we see when someone bends over those where the spinous processes over there that you are going to be seeing on someone’s back.1728

Something like scoliosis would be obvious if you have someone bend over and you look along their back 1737

If their spinous process does not appear to be straight they have scoliosis.1744

You can see that these curvatures 1, 2, 3, 4 is very wavy.1749

From the front and back it should look straight but from the side this help give us our posture.1759

Here is that pelvic curvature.1767

The sacrum and coccyx.1770

The coccyx is a very small portion of it and the rest of it is the sacrum.1773

The reason why I say here that the sacrum has 5 pieces and the coccyx has 4. 1785

When we are born we have a lot more bones than we do as an adult.1789

As an adult we have 206 bones and in some baby bodies if you counted all of them, it would be like 300.1794

A lot of these bones are fusing together to make a smaller number as we age.1801

In adult body you would see the sacrum as one bone and the coccyx as one bone.1806

It is a product of fusing together bones that were previously not connected directly.1811

The sacrum if you count it there is the 5 pieces and they are all fused together here.1818

You can see it says at 25 year.1827

Here is the side view of the sacrum and you could see this little surface here that is where the pelvis or illium would fit into. 1831

The reason why I say the coccyx has only 4 pieces is some people it is only 3 bones and in some people it is 5.1842

Most of the time you would see 4 tiny bones making up that very most inferior part of the vertebral column.1849

The last part of the axial skeleton is the thoracic cage also known as the rib cage.1858

You have 12 pairs of ribs if you count all of them there are 24.1865

You can see how this top rib articulates with the first thoracic vertebra or t1 all the way down to t12.1869

Here where you do not have rib anymore that is the first lumbar vertebra down to the pelvic curvature1879

You got these 24 ribs connecting to the vertebrae and back of the thoracic curvature and they connect to the sternum.1886

The breast bone or sternum has 3 main sections, the first one being the maneubrium.1896

The maneubrium right here is the most superior part.1904

The very first pair of ribs connect to it and also the clavicles connect to it which we will cover more in the appendicular skeleton lesson.1909

The body is the major part of the sternum where a lot of cartilage is articulating with it and that is the major part of the sternum.1919

Finally, the syphoid process.1935

This little guy seems very insignificant but there is a major application with CPR when it comes to this bone.1937

If you take a CPR course on how to properly resuscitate and give compression to somebody, they tell you that when you remove their outer garments1945

and you look at their chest to find the proper spot to give compressions, they want you to find where the lowest ribs come together 1954

then put 2 fingers there and then place your palm above it because if you give compressions to where the syphoid process 1961

is you can break it off very easily if you are giving compression the right way and you can puncture the person long or worse.1971

You would be doing them a service if you try to get them come to and get their heart beating again.1979

they have you do the 2 finger rule so that the bottom of our palm is resting right about there.1985

That is going to be closer to the heart and avoiding the syphoid process breaking off.1992

The last part that I wanted to tell you about is this darker stuff.1999

Even on a real skeleton when you look at them if they are an authentic skeleton that is cleaned and displayed, usually that part of the rib cage will be darker.2010

It is not dried or regular bones, that is dried cartilage and that soft bone tends to be brownish.2023

If it was not for that cartilage we would not be able to do this.2033

It helps the thoracic cage expand and contract much more easily because of that soft bone.2036

The costal cartilage also applies to this other term that has to do with the intercostal spaces because they are between the costal cartilages.2045

The intercostal space also applies to inter costal muscles.2061

Those were the main muscles that are helping you in expanding and relaxing the ribcage.2066

I wanted to point out these ribs at the bottom.2076

They are few ribs that do not come back and connect with costal cartilage and those are called floating ribs.2080

It is tough to find them but they do not come up and connect with other ribs to the body of the sternum.2088

Thank you for watching