The Head: Part One of Oh My Gosh, Who Knows?

The human head is incredibly complex-- certainly too complex to try to write too much about it in one post. When I took gross anatomy in graduate school, we spent as much time dissecting the human head as we spent on the rest of the body. And for good reason. There's just a heck of a lot going on in there. On this blog, of course, we won't be discussing any of the deep structures, like the brain, the twelve cranial nerves, or the elaborate labrynth of cerebral blood vessels. But in this area of the body, even the surface landmarks are packed in. I would like very much to savor them one post at a time, but before we do this, we she should probably start with a head overview. 

The head differs a great deal from the rest of the body, even landmark-wise, because not much muscle shows here. There are muscles that obscure most of the skull, but they are very thin and flat and, as such, don't show much on the surface. Most of the facial muscles insert into the skin (as opposed to inserting on bone) because it's the skin that they move-- for the sake of facilitating facial expression. But most of the muscles themselves don't show up individually.

Sometimes we can see evidence of two cranial muscles, the temporalis muscle and the masseter muscle, because they contract a bit when we are chewing. The masseter, the thickest muscle on the skull, lies over a portion of the mandible, just anterior to the ear, and sometime even its striations can be seen during chewing. The wide temporalis muscle lies on the side of the head, just above the ear, and sometimes we can see it, too, flexing, when an individual is chewing or clenching. 

Movement of both the temporalis muscle and the masseter muscle can sometimes be seen when an individual is chewing. These are among the only muscles on the head that can be identified individually on the surface.

But other than these occasionally visible muscles, most of the head's prominent surface landmarks are bone. We'll cover each of these in future posts. But before we begin this, let's look at the basic structure of the skull.

The skull has two basic portions, the cranium and the facial region. These are good to keep in mind when drawing the head, because each has its own shape and the two together help define the form of the head. The cranium is the oval shaped, hollow portion of the skull that encases and protects the brain. It shaped somewhat like an egg and is tilted upward anteriorly. The facial region of the skull is the area on which the facial features (such as the eyes, nose, and mouth) rest. It's shaped like a mask and hangs off the front of the cranial egg shape. 

The image below shows a lateral view of the skull alone and with outlines of the cranial and facial regions. The cranium is shown in pink and the facial region is shown in blue.

The cranium is the egg shaped portion of the skull than encases and protects the brain. The cranial region of the skull is outlined in pink here. The facial region, outlined in blue, is the mask shaped portion of the skull. It's the area on which the facial features rest.

It's important to consider the shapes of both these regions when drawing the head. The region shapes may also be used to determine proper head proportions and to position the ear. When measuring any human head from its most anterior to its most posterior point, the halfway point almost always falls just behind the mandible and just in front of the ear. When drawing a head, placing a vertical line halfway back on it helps to properly position both the back edge of the mandible and the front edge the ear. This is demonstrated in the image below.

When divided in half from front to back, the halfway way point on the human head falls just posterior to the mandible and just anterior to the ear. This is helpful to know when placing an ear on a drawing of the head. The black lines here show the anterior and posterior halves of the head. The verticle strip of beige shows where tissue depth has been accounted for on the anterior side (since its greater here than on the posterior side.) The red line shows the placement of the ear behind the middle line.

In upcoming posts we will begin examining the individual bony landmarks of the skull more thoroughly. These include the superciliary crests, the zygomatic arch, the mental protuberance, the angle of the mandible, and the occipital protuberance, to name a few. This will take, well, who knows how long? But I don't mind! Do you? 

Sternocleidomastoid: Don't Forget the Cleido!

Just a quick landmark sighting today, and this time on an illustration instead of a photograph. We've already had a close look at the sternocleidomastoid muscle and its surrounding structures in an earlier post, The Anterior Neck: Theme and Variations. But this wonderful rendering by an old pal made me want to revisit Mr. SCM briefly. Shawn Campbell is a talented and prolific artist whose seemingly endless turnout of illustrations have been a great source of inspiration to me ever since we met in Ms. Brackman's seventh grade art class. Thirty-plus years later, Shawn and I continue to share our friendship, our ideas, our rants and, of course, our art, with one another.

One thing I like to stress in my anatomy class is that knowledge of human skeletal and muscular structure is not only useful when drawing realistically but also when drawing a human (or humanoid) with stylized or exaggerated features. Shawn's drawing below demonstrates this beautifully. Let's take a look:

This head drawing, and all of Shawn's figure and portrait studies, show his knowledge of the human form and his ease and comfort in rendering it. Even in this exaggerated head study, it's clear that Shawn understands the structure of the skull, the shape relationships of the external ear, and the nuances of the anterior neck muscles. One anterior neck muscle in particular, the sternocleidomastoid, caught my eye here.

The sternocleidomastoid muscle is named for its points of origin and insertion; its name has three parts (sterno-cleido-mastoid) because this muscle has two origin points and one insertion point. The sternocleidomastoid muscle's origin points are the superior edge of the sternum (sterno-) and the medial end of the clavicle (cleido-) and its insertion point is the mastoid process (-mastoid) which is a bony lump on the temporal bone than can be felt just posterior and inferior to the ear. The bilateral sternocleidomastoid muscles grab the mastoid processes and, among other actions, allow us to turn our head from side to side.

But or some reason, the poor clavicular origin point of the sternocleidomastoid muscle is too often neglected by figure and portrait artists. We all seem to know about the sternal attachment-- most likely because it's more visible-- and we tend to draw it very clearly (sometimes even too clearly.) But very often we completely leave out the clavicular attachment. Which is why I loved this rendering of Shawn's. He didn't forget the clavicular attachment! 

Let's look at the figure again below, but on this one (with Shawn's permission) I've added a little diagram:

The sternocleidomastoid muscle is a bilateral structure, meaning there are two of them-- one on either side of the body's midline. The two sternal attachments of the muscle connect to either side of the jugular notch at the superior edge of the manubrium of the sternum. (The jugular notch is also known as the suprasternal notch, as suprasternal means above the sternum.) This is the attachment we almost always remember to draw. 

The clavicular attachment, however, is often overlooked. As you can see here, it connects to the clavicle and it is generally wider and flatter than the sternal attachment. So from now on, don't forget to draw this lovely little portion of Mr. SCM!

One last note: Your common carotid artery runs right through the little split between the sternal and clavicular attachments of the sternocleidomastoid muscle. So press your finger in there if you want to feel your carotid pulse. Sometimes you can even see your carotid pulse on this spot. That's pretty cool.

Thanks so much to Shawn for letting me use his illustration. If you'd like to see more of Shawn's work, take a look here. I have another old school buddy helping me out with what I hope is the the next post, back muscles. See you then!

The External Ear: Shhh, I'm Listening to Reason!

It stands to reason that a structure's design enhances its function. It stands to reason that its size, shape and materials best suit that function. It stands to reason that, in multiples, that structure has latitude for variability while maintaining the same basic parts. And maybe most of all, it stands to reason that the best examples of such a design would be found on the human body.

While most any anatomical structure could provide a satisfying conclusion to this goofy little rumination, I think one of the most interesting and unique examples is the lovely, complex, variable yet constant structure of the human external ear.

When learning to draw any part of the human body, we're taught, of course, to remember what must always be shown, what is constant. But learning those things shouldn't come at the cost of remembering the variations, the ways in which these structures may differ from person to person. While most human ears can be drawn with the same basic parts and pieces, the relative sizes of and relationships among those pieces can vary a great deal. Drawing the ear becomes much easier (and a lot more interesting) when we remember both the constants and the variables. 

The ear is constructed of an outer rim, the helix, and an inner rim, the antihelix. These two structures form sort of an oblong bowl shape. The bottom of that bowl is the concha; this is the deepest point before we get to the external auditory meatus, the opening in the temporal bone that leads to the middle and inner ear structures. On the anterior side of the ear, there is a small notch (the anterior notch) which lies above the tragus, a small flap of cartilage. One of the most common mistakes in rendering the ear is drawing a connection between the helix and the anterior notch. They don't connect there, but it seems their proximity to one another makes us think they should. The difference can be seen in the illustrations below.

The helix actually arises on its leg from the bottom of the concha, usually very gradually. Then it encircles the entire ear and end at the very bottom, at the lobe. The antihelix appear to emerge from underneath the upper portion of the helix, on two legs. Those legs merge together and the antihelix curves around posteriorly as a single unit until it ends at the antitragus (just opposite the tragus, which is what the name antitragus means.)

In addition to names for external ear structures, we also have names for the spaces and depressions among them. We have the intertragical notch, which is the small notch between the tragus and antitragus. We have the scapha, which is the long valley between the helix and the antihelix. And we have the triangular fossa, which is the depression between the two legs of the antihelix.

By the way, scapha is Latin for boat, and it seems that anatomical structures with a depressed center (like a boat) often have this name or some variant of it. We have a scaphoid bone in our wrist which has a depressed shape. Navicular means the same thing, and we have a navicular bone in our foot that also has a depressed shape.

Most of the above mentioned structures are composed of cartilage, which is the ideal material for the human external ear, as it's flexible but it holds its shape. If it were entirely skin and fatty tissue, it would flop over on itself and lose its satellite dish shape that draws sound waves into the auditory meatus. On the other hand, if the external ear was made of bone, it would hold its shape but it would break easily. So most of the external structure is composed of cartilage, although the lobe is mostly fatty tissue, which is why it's floppier than the rest of the ear.

One of the most noticeable variations in external ear anatomy is that of free lobes vs. attached lobes. This is a genetic trait. Although there's not 100% consensus, it's widely believed that attached earlobes are the recessive trait. If you have attached lobes, this means you most likely have two recessive alleles for it.

Another variation among ears is the depths of the sunken areas. The concha, scapha, and triangular fossa range from very shallow to very deep. In addition, the intertragical notch (the small notch between the tragus and the antitragus) varies somewhat in width from one individual to the next.

I would also like to write about rendering the ear and its shapes from a variety of other angles, but this post has gone on long enough! Shall we save it for another day?

It also stands to reason that my lovely ear models deserve a load of thanks! They include family members, neighbors and students: Daniel, Henry B., Henry G, Hillary, Jeff, Nick, Sean, Stephanie, Theresa, and Thomas.

The Anterior Neck: Theme and Variations

It's difficult to prescribe one exact way to draw the anterior neck because its surface appearance depends on so many variables. Superficial anatomical structures and their degree of visibility change with head position, facial expression, age, body type, and even the level of physical exertion. Today we'll look at these structures and discuss the conditions that affect their visibility.

Typically the easiest landmark to identify first is the jugular notch (a.k.a. suprasternal notch), a small divot on the superior surface of the manubrium of the sternum. On either side of the jugular notch, you will probably see origin tendons of the sternocleidomastoid muscle, as well as the medial ends of each clavicle. One common problem in figure drawings is a jugular notch shown flowing directly into the clavicles. We tend to draw it this way because we know the clavicles connect directly to the manubrium-- but we tend to forget that you can't really see that connection on the surface. Why can't we see it? Because the origin end of the sternocleidomastoid muscle attaches to the manubrium and to the medial ends of the clavicles, and this attachment obscures the connection between the manubrium and the clavicles. The paintings below show the difference.

While the origin end of the sternocleidomastoid muscle (particularly the manubrial attachment) is usually visible as a surface landmark, whether we can see the rest of the muscle depends primarily on head position. We know from its name that sternocleidomastoid originates on the sternum (sterno) and the clavicle (cleido) and inserts on the mastoid process of the temporal bone (mastoid) which is the bony bump you can feel just behind your ear. So if the entire sternocleidomastoid muscle shows, you'll see its split origin end come from the manubrium and the clavicle, you'll see it merge together as it extends superiorly, and finally you'll see it attach just behind the ear. Just behind the ear-- not way behind the ear or under the ear or in front of the ear, all common mistakes in head and neck drawing.

But how do we know whether or not to show the entire sternocleidomastoid muscle? It's also a common mistake to render both sternocleidomastoids from end to end no matter the head position. But the sternocleidomastoid muscles don't always show in their entirity. When they're not in use, the most we'll usually see of them are their manubrial attachments on either side of the jugular notch.

The sternocleidomastoids (herein referred to as SCMs) do show, however, when they're being used, and they have two uses. First, when the SCMs are used together, they hold the head in position when the torso is tilted backward. In other words, you can lean your body backward without your whole head flopping backward because your SCMs, when working together, hold your head in place over the torso. This is shown in the photo below of my lovely neighbor Stephanie.

When used separately, the sternocleidomastoid muscles have another function; they turn the head to the left or to the right. We use the left SCM to turn the head right, and we use the right SCM to turn the head left. As such, if the head is turned to the right, only the left sternocleidomastoid shows, and vice versa. The photo below shows Stephanie with her head turned to her left, so only her right SCM is showing from end to end. The left one is showing, but only at its manubrial attachment.

The SCMs create a sort of V shape on the anterior neck, and there are two more structures inside this V that can often be observed on the surface: First, we have two long thin sternohyoid muscles. As their name suggests, the sternohyoids originate on the sternum (the superior edge of it), extend upward, and insert onto the hyoid bone, a small horseshoe shaped bone in the anterior neck. You can't see the hyoid bone on the surface, but you can just barely feel it if you really dig your fingers into your neck just below the mandible until you're going "gagghhh!"

The sternohyoids run almost parallel, but not quite; they are slightly closer together at their insertion end than at their origin end, as you can see in the photo and illustration below. You usually can't see the sternohyoids in young people, but they begin to appear on the surface in one's 40s. Often neck structures are more visible in older age because fat tissue in the neck dissipates and the skin gets thinner. And often the skin on the neck follows the shape of the sternohyoids more and more with advanced age. So very old individuals will have two long folds down the anterior neck that run right along the sternohyoids.

In between the sternohyoid muscles is another structure that is usually visible on the surface-- the thyroid cartilage, colloquially known as the Adam's apple. The thyroid cartilage is part of the trachea, a cylindrical structure through which air travels from the throat into the lungs. The trachea is made up of a series of cartilaginous rings, bound together by connective tissue. The thyroid cartilage is the most superior ring of tracheal cartilage. It is much larger and more prominent than the rest, and as such, tends to poke out through the neck.

The ring of thyroid cartilage houses the larynx, in which our vocal chords are found. Men typically have deeper voices than women because they have larger larynges and larger vocal chords. This means they also have a larger thyroid cartilage in which to house them. This is why the thyroid cartilage is generally much more visible on a man's neck than on a woman's.

Just below the thyroid cartilage, there is another ring called the cricoid cartilage. This is not as large or prominent as the thyroid cartilage, but it can often be seen on the surface as well.

When observing the anterior neck you might also see the external jugular veins, bilateral vessels that return blood from the head to the heart. In certain situations you might see them popping out on the neck. Each one runs right over the SCM at an oblique angle to it. There's usually no need to show them in a drawing, though, unless your subject is exerting a great deal of physical energy (or is just really mad!)

There is another very thin anterior neck muscle that lies superficial to all of this-- the platysma! But its appearance is fleeting, and I've rambled on long enough now, so we'll leave that for another day.

Bonus question: As I mentioned above, the sternal/clavicular end of the sternocleidomastoid muscle is its origin. The mastoid process of the temporal bone is its insertion. Does anyone know how we know this for sure? If so, post below!