Saturday, September 22, 2012

The Temporal Line: There's a Kansas City That Isn't In Kansas

Now that we've covered basic head anatomy in The Head: Part One of Oh My Gosh, Who Knows?, we're ready to observe the individual bones and landmarks of the skull. The first rule of thumb to establish is that bony landmarks of the head tend to be more prominent and visible in adult males. This is especially evident in the superciliary crest (a.k.a. brow ridge), the mental protuberance (a.k.a chin bump), the zygomatic arch (the bony ridge along the cheek) and the temporal line, which we'll look at more closely today.

The temporal line runs along the side of the head across two separate bones-- the frontal bone, which forms the forehead, and the parietal bone, which, with its bilateral twin on the other side, forms the "roof" of the head. 

The temporal line's name can be a little confusing for those first learning about skull anatomy, because we also have a temporal bone (shown in blue below). But, just to keep you on your toes, the temporal line is not on the temporal bone. The temporal bone, which is also bilateral, lies lower down on the side of the head. It's the bone on which the external ear rests, and in which the delicate inner ear structures lie. It's quite an elaborate cranial bone, so we'll take time to look at it and its many surface features later.

This whole situation was summed up nicely by one of my anatomy students last spring. Several students were quizzing one another in preparation for an upcoming skull test, and as they reviewed the temporal line, one said, "the temporal line is not on the temporal bone-- kind of like there's a Kansas City that isn't in Kansas." Indeed!

So let's take a look at the structures involved:

The temporal line (shown in red dashes) is a subtle ridge that runs across the frontal bone (shown in green) and the parietal bone (shown in peach). The temporal bone is shown in blue, but the temporal line does not run across the temporal bone.

Several anatomical structures in this area of the head have all or part of the word temporal in their names. The temporal line, the temporal bone, the temporal fossa (which is the shallow depression on the side of the cranium), the temporalis muscle (a muscle that rests in the temporal fossa), the temporal lobe of the brain (which is the part of the brain that lies on the sides of the head), and several temporal arteries and veins (blood vessels that run through this area). The only of these that we can observe directly on the surface, though, are the temporal line and the temporalis muscle (which we can sometimes see moving when an individual is chewing.)

The slightly sunken area on the lateral skull, just below the temporal line, is known as the temporal fossa.

The temporalis muscle rests in the temporal fossa, just below the temporal line (shown with a red dashed line). The movement of this muscles can sometime be observed when the figure is chewing.

As you can probably guess, most of the temporal line is obscured by hair (unless, of course, the individual in question is losing said hair). At its anterior end, though, it often shows up on the sides of the forehead, where hair would not get in the way. This is one of the skull landmarks that seems to be more prominent on older males-- particularly the bad guys in comic books. (Google Professor X to see what I mean.)

If you look around a little bit, you should have no trouble seeing examples of the temporal line. Even on an individual with a full head of hair, look for a ridge on either side of the forehead, positioned at the same degree laterally as the outer edges of the orbits.

What did I say about older males? Just take a look at Fred Thompson's temporal line. And really, next time you see your dad, take a close look at his forehead. There's a very good chance you'll see at least part of his temporal line. Perhaps all of it, if he's losing his hair!

Older males do not, however, hold a monopoly on the temporal line, as this photo of a bald Britney will demonstrate. She has quite a few prominent skull landmarks, so we'll revisit this image soon. And you thought her abs were defined!

Uncle Fester can join the fun, too. Not much hair blocking this one.

Hey, even individuals sewn together from spare parts can have a temporal line. Dr. Frankenstein was clearly meticulous in his attention to head detail.

The great Oz has spoken! His temporal line rules all! It's prominent as well as quite elaborate. Enough so to have haunted me as a child, anyway. Did anyone else worry that this guy was going to show up in their closet when they were trying to fall asleep?

And finally...

Here is one last shot of the temporal line, this time on my pal Tim. This is from my book, The Figure Artist's Book of Anatomical Landmarks, for which Tim was kind enough to pose. Tim is an accomplished a capella singer, so be sure to check out his group Chicago Voice Exhange!

Well, I think we've about exhausted this topic. Next time we'll either cover more head landmarks, or possibly to finish up one of the other several areas we've begun. Until then, go out and look for some temporal lines! They're everywhere! Even Kansas City.

Monday, August 6, 2012

Human Anatomy for the Artist at Chicago Comic Con

Just a quick post to let you know I'll be at table 3138 at the Chicago Comic Con this week, August 9 through August 12. I'm very happy to be sharing a table with Spiro's Greek Myths, a wonderful comic created by my friend Spiro Dousias.

Spiro will be selling his awesome comics about ancient Greek myths as well as his paintings and action figures of Greek gods and goddesses. I'll be selling my handy little anatomy book, The Figure Artists Book of Anatomical Landmarks. This is a good time to get yourself a copy without having to pay any pesky shipping fees! Also, bring your figure drawings by my table, and I'll be happy to check them out and answer any anatomy questions you might have.

I hope those of you planning to attend the Con will stop by and say hello. I'd love so much to meet you in person!

Thursday, July 19, 2012

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? 

Tuesday, July 10, 2012

The Figure Artist's Book of Anatomical Landmarks: Here's the Order Form!

It's finished! After hours of proofing, re-proofing, uploading, re-uploading, fretting, panicking and just plain waiting, my 375 crisp, clean copies of The Figure Artist's Book of Anatomical Landmarks are back from the printer! And they may now be purchased via check, money order or with a credit card using the link below.

The Figure Artist's Book of Anatomical Landmarks is $21.95 + 2.55 shipping and handling, if shipped within the continental US. Shipping rates on overseas book orders vary. Please email me directly at for shipping rates if you are ordering from outside the continental US. More information about the book can be found below.

If you'd like to pay by check or money order, please contact me directly at for instructions. And if you'd like your book signed, use this email address to let me know!

The Figure Artist's Book of Anatomical Landmarks is a quick reference guide to help the artist identify and understand the lumps, bumps, creases and depressions on the human body. Its clear, concise text and dozens of labeled photographs are organized by body region for handy reference. Its small size and soft cover make it convenient and portable, whether keeping it on your drawing table or taking it along to life drawing sessions. It is 7" x 7", 48 pages, black and white, with a soft cover. This book is best used in conjunction with more traditional anatomy books, as it is not a book of anatomical diagrams. It's consists primarily of figure photos with the anatomical surface landmarks labeled and accompanying descriptions of each, much like those seen on this blog. Here are two sample spreads, which are indicative of just about every page in the book.

 Thank you for your order! I am grateful and humbled by your support!

Tuesday, June 12, 2012

My New Baby! (Don't Call it Ugly.)

The first proof is in! It's small, it's one color, and some might even call it, um... ugly. But hey, it only had a three week gestation period. As its proud mother, I think it's beautiful, and I hope you will, too. (Or you could always lie to me.) In any case, it's packed with information, and I think it will be a very helpful resource to any figure artist exploring anatomical surface landmarks.

One thing I will admit, though, is that I'm going to have to spring for better quality paper. The stock I used for the proof just isn't working; it's super absorbent and the photos got so muddy. And the stock change will mean a change in layout as well. To make a long story short, the current book size won't allow for any other stock. So I have to do some rearranging. This means the book won't be printed quite as soon as I thought, but it should still be done by sometime in the next two weeks. I will post details as soon as possible!

Sunday, May 27, 2012

I Hope Print Isn't Completely Dead Because I'm Making a Book!

A recent occurrence in the life of a friend (to be elaborated upon later) spurred an unexpected dive into a project I've been thinking about for years. Writing and diagramming for a blog is all fine and dandy, but despite my love of electronic media and its infinite educational possibilities, I still have a soft spot for print. So I've always dreamed of creating a book. A book with thick creamy pages that smells like a printing press. A book I can crack open for the first time and run my fingers over after hugging the UPS guy and dragging my eagerly awaited shipment box into the house. Until recently this dream has been next to impossible without an official publisher, but now that the printing process has evolved beyond the expensive and limiting, it's possible for us less-than-famous-or-well-known-or-prolific writers to get some of our own goofy little projects printed.

As such, I'm inhaling deeply and jumping into the world of print-- for a short time anyway. Yep, I'm making a little booklet of anatomical landmarks references for figure artists. It will include diagrammed photos, illustrations, and concise explanations of labeled structures. Its intended purpose is to function as a handy reference guide for figure artists who are stuck on any particular area of the body and would like some extra anatomical guidance.

The book will be organized by body regions, including head, neck, shoulders, anterior, lateral, and posterior torso, upper arm, forearm, hand, hip, thigh, lower leg, and foot. Heck, I may even throw in an ear and eye page is there is enough space. Each area will be shown from a variety of angles and everything will be labeled clearly and thoroughly.

Below is a sample photo from the book, showing the axilla and medial upper arm. It also shows one of my cabinets and some dishes in it because, yeah, I'm not a professional photographer. No matter, we can see lots of anatomical structures, right? Not sure if this specific image will make it into the final cut (I'm still shooting and slashing and re-shooting and editing) but we'll see. Regardless, why don't we take a little time now to talk about what we're seeing here?

OK, first a word about the weird numbering. In this image, I used the same numbers as in another photo on the page (in which they are in order.) Ah, it'll make sense when it's in print. I hope!

The axilla (the anatomical term for the armpit) is formed by two muscles-- the pectoralis major (10) anteriorly, and the latissimus dorsi (11) posteriorly. Up inside the axilla, we can see a short muscle called coracobrachialis (12.) It is given this name because it runs from the coracoid process on the antero-superior scapula down to the humerus bone in the upper arm. (The Latin root brachio- refers to the upper arm.)

Just before coracobrachialis inserts on the humerus, it tucks under biceps brachii (4), the most obvious superficial muscle on the anterior upper arm. Just deep to biceps brachii at its distal end is the brachialis muscle (13) which can be seen peeking out on either side of biceps brachii (although its borders are not very obvious here.) We can also see the long (8) and medial head of the triceps on the medial upper arm. The only bony landmark we see on the medial upper arm is the medial epicondyle at the distal end of the humerus. Another visible structure in the area is the deltoid muscle (3) that covers the top of the shoulder.

Just posterior to the coracobrachialis (12) we can see another soft lump of tissue labeled with an F. This is not a muscle, but a small mass of fat tissue that cushions and protects a few structures that course through the underarm, including the basilic vein, the median and ulnar nerves, the brachial artery, and some lymph nodes, which feel like lumpy little jelly beans in the armpit.

There are also a few structures in the image that, while unrelated to the upper arm, warranted acknowledgment for their clarity. Those are the clavicle (C) and the sternocleidomastoid (SCM) muscle on the anterior neck.

The book should be printed and on sale by sometime in June! I will post more information then. See you next time!

Friday, May 18, 2012

Vestigial Traits: You May Not Need Us, But We're Still Here

Short post today. I have a side project in the works, the details of which are soon to come! Until then, how about a short post about human vestigial traits! 

Because my anatomy course is for art students, its content is designed almost entirely around the human body's superficial structures-- mostly muscles and bony landmarks-- that dictate the external human form. But occasionally (well, OK, often) we go off on random tangents during which students asks about other anatomical structures or physiological processes. And I have to admit, these random questions are one of my favorite parts of the class.

One subject that comes up often is that of human vestigial anatomical structures. Vestigial structures are those that had a purpose in earlier evolutionary forms of ourselves, but now have little or no function. As evolution allows us, as a species, to slowly adapt to our environment and our circumstances, certain structures become unnecessary. With each generation these structures become slightly less prominent, until they are slowly phased out altogether. Our vestigial structures (and reflexes, for that matter) are those which still remain in some form but no longer serve much of a purpose. One example is our coccyx bone, which is the remains of what use to be caudal vertebrae, or bones of a tail.

Here is a nice summary of ten vestigial traits that still occur in humans today. Enjoy, and I will be back soon with a new posterior torso post as well as more news about my new project!

Thursday, May 3, 2012

The Annular Ligament: Full Circle!

It's a big day here today-- it's Human Anatomy For The Artist's first anniversary! Yep, it was one year ago today that the debut post, The Ventral Forearm: What are those Tendons? went live. Today, 366 days, 28 posts, and 80,314 page views later, I am happy to say that my goofy little blog is still going strong. As of this morning, Human Anatomy for the Artist has 89 Blogger followers, 51 Networked Blogs followers, and 2,032 Facebook followers. Writing and drawing about this topic is such a great joy, so I want to thank you for all the wonderful forms of encouragement, including your regular visits, words of gratitude, and messages from around the world. It's so gratifying to know that people are learning from these posts. Please keep spreading the word as we head into our second year!

Year 2 dangles many new post ideas before us; there are so many structures and concepts I still want to cover. It is quite awesome (and reassuring somehow) that a finite science like Anatomy can still have such vast depth. I can't imagine trying to write about a subject such as space or philosophy, whose possibilities are truly endless, without going a tad crazy.

The fact that we've come full circle today gave me the idea to write about an anatomical structure that also comes full circle. The annular ligament is named for its circular, or ring-like structure; the Latin word anulus means ring, so annular means "ring like." Quite fittingly this morning, both the words annual and anniversary come from a related Latin root; when an event is annual, it has come full circle from the previous year. Like the annular ligament, this blog comes full circle today. And even more fittingly, this structure was discussed in the very first post a year ago today.

Here is the image from that post again, with only the ligament and some related tendons labeled. Before going further, I should point that this particular annular ligament is not the only one in the human body. This name is given to most any ring-shaped ligament, and this is just one of at least five. As you can see, this one is located at the distal forearm. (Some of the others are located on the proximal radius, the ankle, the knee, and the trachea.)

The annular ligament in the wrist isn't something we artists think about much when we draw the human figure. You can't really see it on the surface. But it does affect surface appearance. There are two fairly visible tendons on the ventral wrist, the tendon of flexor carpi radialis and the tendon off palmaris longus. The tendon of palmaris longus is usually more visible than that of flexor carpi radialis because it runs outside the annular ligament. So if you're drawing the two ventral wrist tendons, it's important to make sure the correct one is more visible. Palmaris longus, the more visible of the two, is closer to the ulnar (pinky) side of the hand. This is explained in much more detail in the first post from one year ago, and some photographic and illustrative examples are shown there as well.

The function of the annular ligament on the distal wrist is to retain the position of the long forearm tendons that reach into the hand (with the exception of the palmaris longus tendon, whose distinction is its unique course outside the annular ligament.) This annular ligament's function is reflected in its more commonly used name, retinaculum. This term comes from the Latin retinere, which means to hold back.

Thank again for sticking around for the past year, and I look forward to working on upcoming posts! There are several series from the past year that need to be continued, including those on direction and location, back muscles, and the elbow joint. More in those series to come soon, plus more new material. See you soon!

Friday, April 27, 2012

Student Work! A Sneak Preview with Bad iPhone Shots

The Spring semester has just ended at the American Academy of Art, and over the past few days I've had the pleasure of looking through all the lovely anatomical drawings my Advanced Anatomy students did this semester. I would like to scan and post some of my favorites over the summer, but for now I'm going to offer a little sneak preview. I'm sorry about the quality. These were taken with my iPhone in the midst of a grading frenzy.

Justine Herrera's rendering of anterior neck muscles.

Chase McNicholas's rendering of anterior torso muscles.

I will post many more images soon, after I sleep for about 15 hours and then do some scanning! Thanks, Justine and Chase.

Friday, April 20, 2012

Quick Forearm Study: My Pal Rich

Here's a quick forearm muscle study using my pal and fellow illustration instructor, Rick Kryczka. We see mostly the extensor/supinator group here, which is discussed more thoroughly in The Dorsal Forearm Part 1: Compartment Search, The Dorsal Forearm Part 2: Which Side Are You On, Anyway?, and The Dorsal Forearm Part 3: The Final Chapter. There are also smaller updates on this area in The Dorsal Forearm: One Last Encore and Landmark Sightings Part 1: Bruce Lee. 

You might start orienting yourself on this image by first identifying the olecranon process of the ulna and the lateral epicondyle of the humerus. From there you can identify anconeus, the small triangular elbow muscle that originates between those two landmarks and then points into the crease between the extensor and flexor forearm muscle groups groups. (And if you keep following it distally, will take you to the crest of the ulna.) From there you can identify the twin muscles (extensor carpi ulnaris and extensor digitorum) and then extensor digiti minimi between them, and so on. The links mentioned above explain all this in much greater detail.

Bony landmarks to find first: lateral epicondyle (LE), olecranon process (OP), and the ulna itself, whose crest
and head show at the distal and of the arm. The extensor muscles will follow: Anconeus (Anc), extensor carpi
 ulnaris (ECU), extensor digitorum (ED),  extensor carpi radialis brevis (ECRB), extensor carpi radialis longus
(ECRL), and brachiradialis (Brr). Some thumb muscles can also be seen: Abductor pollucis longus (APL),
extensor pollucis brevis (EPB) and the tendon of extensor pollucis longus (EPL.) Finally, a few upper arm
muscles are shown: Biceps brachii (BB), brachialis (Br), the lateral head of the triceps (Tlat) and the triceps
tendon (TT).

Friday, March 30, 2012

Posterior Torso Muscles, Part 2: Under the Radar

You may have noticed that I keep describing the forearm as the most difficult part of human anatomy to teach (and the most difficult to understand!) This area is so difficult for some pretty straightforward reasons: 1) There are so many forearm muscles, and 2) they all look very much alike. But sometimes I forget that the posterior torso muscles, although they are large and varied, are also among the most difficult to understand. In my class, they sometimes require as many days to get through as the forearm muscles. But the posterior torso muscles are confusing for a completely different reason-- unlike most muscles that concern the figure artist, they like to live under the radar.

Like most areas of the body, the posterior torso has several layers of muscle. When rendering most areas of the body, we artists tend to think primarily about the superficial muscle layers-- the ones that are visible at the surface and contribute most to the body's outward appearance. But things are a little different on the posterior torso. Its muscles are exceptionally broad, thin, and flat, which means we sometimes can see deeper muscles showing right through them. This is pretty cool, but it does make things a little more confusing.

In fact, sometimes the deeper muscles of the posterior torso show more clearly on the surface than the superficial muscles. How can that be? This happens because the superficial muscles are often so thin and flat that they just don't look like much on the surface. But the muscles underneath them are rounder and more defined, so it's actually easier to pick out their shapes. 

There are some wonderful examples of this in the figure renderings of Brian Skol. Brian is a student at the Ravenswood Atelier in Chicago, and during his time there he has developed a solid, stunning figure drawing technique and turned out an impressive collection of work. Brian also took my Anatomy course at AAA several years back, and while he is among several top students who mastered the class, he is distinctive in that he's the only one who's ever said the Anatomy final exam was not difficult enough! This comment was unexpected and refreshing, as I'm used to hearing just the opposite.

Several of Brian's figure drawings lovingly demonstrate the posterior torso landscape, but today (and in a few upcoming posts) we'll concentrate on this one. First let's look at the subtle ridges that help define the structure of the back.

Each of the skin ridges in Brian's figure drawing subtly reveals a muscular relationship on the posterolateral torso. Ridge 1 shows the point at which the latissimus dorsi meets the lumbar sheath. Ridge 2 demonstrates the furrow at which the external oblique muscle meets the rectus abdominis muscle. Ridge 3 shows where the serratus anterior muscle travels back toward its insertion on the underside of the scapula. (It's actually under latissimus dorsi at this point, but we can still see it because latissimus dorsi is so thin.) Ridge 4 shows the teres major muscle as it extends laterally toward the upper arm, where it will insert on the anterior side of the proximal humerus. The lower edge of teres major is hidden under latissimus dorsi, but it still shows. Finally, ridge 5 shows the posterior edge of the deltoid.

I know, I know. I did say subtle, right? But part of the beauty of the human body is that so much of it is a mystery; its structures are always there, doing their job, making things happen, but many don't necessarily need to be right in your face; they'd prefer to stay under the radar and let you discover them. 

So let's take a closer look at these shy little devils. The first step in this process was to block in some overall muscle shapes and a few bony landmarks, then to identify them.

Drawing in these basic structure shapes was the starting point for exploring each of the posterior torso ridges more closely. The iliac crest is shown in yellow but unlabeled. The large posterior torso muscles are trapezius (T) and latissimus dorsi (LD). Together with deltoid (D), they form a triangular window, in which we can see infraspinatus (Inf) and teres major (TM). Teres minor is barely peeking out between infraspinatus and teres major, but I didn't label it. Just anterior to latissimus dorsi, we can see two anterior torso muscles: external oblique (EO) and rectus abdominis (RA). I've also included some structures just under the iliac crest: Gluteus maximus (Gmax), gluteus medius (Gmed),  and tensor fasciae latae (TFL) all surround the greater trochanter of the femur (GT). Distal to that we can see vastus lateralis (VL) and the iliotibial band (ITB).

Now let's take a look at the ridges that are so beautifully and accurately rendered in Brian's drawing. We'll start with ridge number 1, where the lumbar sheath meets the latissimus dorsi muscle. First, here's how these structures look from a direct posterior view.

The lumbar sheath is a flat, diamond shaped aponeurosis covering a large portion of the lower back. It serves at an origin point for the large, bilateral latissimus dorsi muscles. We can often see a ridge along the lower back where these two structures meet. Note that both latissimus dorsi and the lumbar sheath have been removed on the right side of the body in this image.

You might recall this image from my first posterior torso post. At that time we looked at the relationships of the larger back muscles and the small triangular window they form (in which we can see some smaller muscles on the posterior surface of the scapula.) Now let's use this image to look at the landscape of the lower back. Occupying most of its space is the lumbar sheath, a diamond shaped aponeurosis (which is broad, flat, tendinous muscle covering.) The lumbar sheath serves as an origin point for the large bilateral latissimus dorsi muscles that run across the lower back and sides. Because the lumbar sheath is not muscle tissue, doesn't bulk up with use. So it can appear somewhat flat in comparison to the lumbar sheath. This means we can often see a ridge where these two structures meet. That's what we're seeing on the area labeled number 1 on Brian's drawing.

In this next image, the basic shapes of latissimus dorsi and the lumbar sheath are placed on top of Brian's rendering. This shows the placement of the individual structures and their meeting point. 

The lumbar sheath (shown in white) is an origin point for latissimus dorsi (LD). Because the lumbar sheath is flat and the latissumus dorsi has some bulk, we can often see a ridge on the back where the two meet. This ridge forms one of the upper edges of the lumbar sheath. The lower edges are formed by a small corner of the external oblique that reaches around to the back and attaches to the iliac crest.

We can see here that both the latissimus dorsi muscle and the external oblique form borders around the lumbar sheath. The angles of these borders give the lumbar sheath its diamond shape. On a more muscular individual, the flat lumbar sheath would stand out more obviously against the surrounding muscles and would become even more visible.

I am looking forwarding to explaining the other four ridges that can be seen in this lovely rendering, but this is getting a little long, so I'm going to sign off for now. I will cover ridges 2 through 5 in an upcoming post, and I'm also working on the rest of the elbow joint posts. See you soon! 

Friday, March 9, 2012

Batman's Anterior Thigh Compartment

So... I saw this photo and couldn't resist diagramming it out. We haven't covered the anterior thigh on this blog just yet, but do not fret, my anatomy friends! It will come very soon. For now let me just explain the muscular organization of the thigh. First, the photo:

Batman certainly uses his anterior thigh muscles when rollerskating. I mean, look at that definition! When I saw this photo awhile back, it went right into my "Must Diagram" folder. Because it provides a wonderful, clear example of the anterior thigh landscape in a weight bearing leg.

The human thigh is divided into three muscle compartments. Within these compartments are specific muscle groups. The difference between a muscle compartment and a muscle group is this: A muscle compartment is based on location (such as anterior compartment, posterior compartment, etc.) and a muscle group is based on function (such as flexor group, adductor group, etc.)

The human thigh has three muscle compartments, and each of these compartments has its own muscle group:

• The anterior compartment (on the anterior side of the thigh) houses the leg extensor group (the muscles that extend, or straighten, the leg at the knee joint.)

• The posterior compartment (on the posterior side of the thigh) houses the leg flexor group (the muscles that flex, or band, the leg at the knee joint.)

• The medial compartment (on the medial side of the thigh) houses the leg adductor group (the muscles that adduct the thigh, or pull it inward toward the midline. More about the midline here.)

There is no lateral compartment on the thigh, although there is one structure on the lateral side of the thigh that does not belong to any specific compartment-- the iliotibial band. We can see the iliotibial band when drawing the figure and we discussed it briefly in a previous post, The Lateral Knee: A Change of Scenery. In the photo shown here, we can also see tensor fasciae latae, the muscle responsible for tensing the iliotibial band, on the lateral side of the thigh. (Tensor fasciae latae means tensor of the wide band.)

OK, let's diagram this thing out:

Here we see three muscles of the thigh's anterior compartment, plus a few other structures. (As a side note, there are actually four muscles in the anterior compartment, but one is not superficial so we can't see it.) The three anterior compartment muscles that we can see here are rectus femoris (a bipennate muscle that runs down the middle of the anterior thigh, directly above the patella,) vastus medialis, and vastus lateralis. The fourth anterior compartment muscle, which we cannot see on the surface, is called vastus intermedius.

Because there are four muscles in the anterior compartment that all insert into the same tendon, they are often collectively referred to as the quadriceps, which means four-headed muscle. And the tendon into which they insert is called the quadriceps tendon. You might sometimes see this referred to as the patellar tendon, as it attaches superiorly to the patella.

There will be more detailed thigh posts later, in which we'll explore each compartment much more thoroughly. But next time, we'll be returning to the elbow joint. See you then!

Friday, February 24, 2012

The Elbow Joint, Part 1: Anterior View, Supine Position

One of the nicest things about teaching at an art college is meeting dozens of new students every year, getting to know them, and often forging friendships that last long after graduation. Being a teacher of both anatomy and illustration means sometimes my students do unusually interesting and creative things for me, like making me little anatomical drawings (sometimes on the backs of quizzes,) alerting me to interesting anatomy-related links like this one or this one, or sending me images they think I can use for my blog. 

Last month I was fortunate to receive a nice collection of x-ray images from former student Bob Giova, who graduated from The American Academy of Art several years ago with a B.F.A. in watercolor. Bob was in one of my first anatomy classes-- quite possibly the very first semester I taught there. He was one of those students who aced every quiz and exam without breaking a sweat. We have kept in touch over the years, and recently he was kind enough to send me images of some x-rays he'd had taken of his forearm. This couldn't have come at a better time. I'm short on back muscle photos, and this gives me something else to write about while I address that. The elbow joint! We'll return to the back muscles later.

The elbow joint is one of the most complex in the human body. Most skeletal joints involve only one articulation (an articulation is a place where two bones meet) but elbow joint involves two. This is why we can produce two different arm movements there. But before we talk about that, let's look at the bones involved:

The bones involved in the elbow joint are the humerus, radius, and ulna. The radius is on the thumb side of the arm, and the ulna is on the pinky side.

The three bones involved in the elbow joint are the humerus (in the upper arm) and the radius and ulna (in the forearm.) The first thing I like to teach students about the radius and ulna is how to quickly tell them apart. The easiest way is to remember that the radius is always on the thumb side of the forearm and the ulna is always on the pinky side. This remains constant no matter the position of the hand because the hand moves with the forearm bones. More on this later. If you're looking at an image of the radius and ulna in which you can't see the wrist and hand bones, you can still tell the radius from the ulna: The radius is wider and its distal end, because it has a broad articulation with the bones of the wrist (the carpal bones.) The ulna is wider at its proximal end, where it has an intimate articulation with the humerus. That articulation will be examined more closely later.

Here is a closer look at the elbow joint itself:

The trochlea (at the distal end of the humerus) rests in the trochlear notch of the ulna. This is the articulation where are flexion and extension occurs. There is also an articulation between the proximal ends of the radius and the ulna. This is where forearm supination and pronation occurs. (Supine position is palms turned up; prone position is palms turned down.) By the way, that thin membrane between the two forearm bones is called the interosseus membrane. Inter means between and osseus refers to bones, so this name just means "membrane between bones."
The above image shows the two separate articulations at the elbow. One articulation occurs where the trochlea-- the wide, spindle shaped structure at the distal end of the humerus-- rests in the trochlear notch-- a wide depression in the proximal end of the ulna into which the trochlea fits perfectly. The proximal end of the ulna has sort of a wrench shape (the sunken area of which is the trochlear notch) and its back and forth turning motion around the humerus is what produces the flexion and extension movements (or bending and straightening) of our arm.

As you know, though, this isn't the only way our elbow joint moves. We are also able to pronate (turn our palm downward) and supinate (turn it upward.) This twisting motion of the forearm allows us to turn our hand all the way forward or backward without having to turn our body around-- or our upper arm for that matter. We're capable of independent pronation and supination of the forearm because of the proximal radioulnar articulation-- the articulation at which the head of the radius spins against the ulna and allows its twisting action. 

There will be more on pronation and supination in a future post, but for now I'd just like to take a look at the appearance of the elbow joint when the forearm is in supine position. 

Anterior view of the elbow joint with its two articulations: 1) Humero-ulnar articuation, where we flex and extend the arm; 2) Radioulnar articulation where we pronate and supinate the forearm. The medial epicondyle is also pointed out, as this is a surface landmark we might see and draw on the arm.

Bob's anterior elbow films allow us to see the relationship between the bones in the elbow joint and the soft tissue surrounding them. The image above shows us why the medial epicondyle is such a prominent surface landmark. You can see the soft tissue of the surrounding skin and how close the medial epicondyle somes to the surface.

Incidentally, the laterial epicondyle of the humerus is also a surface landmark, but it doesn't show from the anterior view. It shows from a lateral and/or posterior view, and when the arm is extended, it tends to look more like a dimple. But we'll look at that later, too.

Bob's x-ray image superimposed over my arm. Cool! This can be done pretty easily because our bone shapes are quite consistent from person to person. Notice how the medial epicondyle comes right to the surface and forms a bump on the medial elbow.

Finally, the above image shows anterior view of the arm with the forearm in supine position. The x-ray image has been superimposed over the top so we can see where the bones fall in the elbow joint. See how the medial epicondyle comes right to the surface and forms a bump on the medial elbow? This photo also shows two visible ventral wrist tendons, those of the palmaris longus muscle and the flexor carpi radialis muscle. These are covered more thoroughly in my very first blog post, The Ventral Forearm: What are those Tendons?

In an upcoming post we'll view the elbow joint from the lateral aspect, examine the landmarks that are visible laterally, and look at the mechanics of flexing and extending the elbow.

Thanks, Bob Giova, for the arm x-rays! We'll be seeing more of them in the next elbow post. To see Bob's lovely watercolor work, go here. See you next time.

Monday, February 20, 2012

Quick Mini Quiz!

There is something wrong with this skeleton. Can you guess what it is? He he he.

Sunday, January 29, 2012

The Posterior Torso Muscles: Let's Go *Back* in Time. Get It?

Hello, all! My apologies for the long wait on this back muscle post, but my search for suitable posterior torso photos has been frustrating to say the least. Let's just say it's not easy to get friends, male or female, to pose topless for me. They're just not those kind of people. At least not since college. But my quandary serendipitously coincided with a massive office clean up during which I came across a dusty old hardbound book. The kind that you know used to have a paper jacket but now has only a cloth cover with gold embossed lettering. The title? Atlas of Anatomy for Artists. Copyright 1947, by Dover Publications, Inc. A true relic of the past!

You know the type of archaic artist's anatomy book I'm talking about-- one color printing on thick creamy paper, formal diagrams labeled entirely in Latin, black and white photos in which the models are haunted, anemic looking creatures with little black triangles covering up their genitalia. Or in which the genitalia are awkwardly airbrushed out so the model, no matter which sex, has the anatomy of a Ken doll. Or in which the model, wishing his or her identity to be hidden, is wearing some sort of blindfold, giving the whole thing a vague interrogation quality. This awkward modesty may seem quaint to us now, but back then it was a necessity. That type of anatomical detail would have earned a book a place in the XXX section of the local paperback grotto.

Is it an art anatomy book or a an advertisement for Interrogation Barbie and Firing Squad Ken? In 1947, it wasn't easy to tell the difference.

The quotes in this book are priceless. One reads "The anatomy of the female differs from that of the male in that the fatty tissue is better developed in the thighs and buttocks." Um, I guess that's one way of putting it. Another gem: "Plate 100 shows a well-built female with almost normal proportions." I'll bet that description made the model's day. Oh, Mr. Author, she might look completely normal if she didn't have one of your old gym socks tied around her eyes.

But I haven't gotten to the best part. Inside the front cover is the handwritten name of the original owner and her art school: Helen Davis, American Academy of Art, Chicago, Ill, 1950 – 51. My mom! Yep, my mom not only went to art school in the early 50s, but she went to the same school at which I teach anatomy today. I find this pretty cool.

My mom's name written in her first art anatomy book. Must ask her who this Buck person was. Did my father know about this?

In any case, the unearthing of this book from my 12 years of accumulated office junk came just in time. I've been wanting to do a post about back muscles, but I've been having a very difficult time finding photos that will show you all the visible surface landmarks. It turns out this book had several nice, clear (albeit archaic looking) posterior torso shots. I don't think they're quite enough, but we can at least begin here.

Shall we start with a quick overview?

On the left side of this figure, only the larger back muscles, trapezius and latissimus dorsi, are shown. We can also see the detoid, a large shoulder muscle on the side. The borders of these three muscles form a little triangular window through which three small muscles peek. Those muscles are not shown on the left side, however. On the right side we see them completely exposed. The blue dashed line indicates the triangular window through with they peek.

The posterior torso, like most areas of the body, is covered by several layers of muscle. But the surface landmarks her are a little more complicated than in other areas because the most superficial back muscles are so thin... and this means many of the deeper back muscles show at the surface as well. It's going to take more than one post to explain this, so we'll start today by looking at the superficial muscles only.

In order to become oriented on the back, it helps to find the largest muscles first and then move on to their smaller counterparts. The two largest muscles in the back (that, in fact, together cover most of the back) are the trapezius muscle and the latissimus dorsi

The trapezius is a diamond shaped muscle that covers most of the upper back. It's long midline origin attaches to nineteen vertebrae!-- C7 all the way down to T12. Its two lateral points attach to either scapula (the spine of each scapulae, to be specific,) its upper point attaches to the occipital bone on the posterior cranium, and its lower point attaches to the spinous process of the T12 vertebra.

The latissimus dorsi is a bilateral muscle that covers most of the lower back. It originates at the lumbar sheath, which attaches to the lumbar vertebrae and part of the sacrum. The latissimus dorsi's fibers converge as it travels upward toward its insertion on the proximal anterior humerus. As it reaches for the humerus it forms the back wall of an underarm depression called the axilla (which is more commonly known as the armpit.)

On this figure's right side, we can see the three posterior scapula muscles that peek through the triangular window formed by the larger muscles. These muscles are infraspinatus (whose name indicates its location inferior to the spine of the scapula) teres minor, and teres major. Teres minor, the smallest and deepest, tends to get squeezed out of the picture more often than not.

 The borders of the trapezius, the latissimus dorsi, and the deltoid (the large muscle on the shoulder) form a nice little triangular window on the posterior torso. Through this window peeks three smaller back muscles, infraspinatus, teres minor, and teres major. These muscles lie on the posterior scapula and are mostly used to adduct and rotate the upper arm. The key to finding these three posterior scapula muscles is first locating the triangular window formed by deltoid, trapezius, and the latissimus dorsi, and then looking inside it. 

Of these three posterior scapula muscles, the most superior (infraspinatus) and the most inferior (teres major) show most clearly, and they are the largest and most superficial. Teres minor, the smallest and deepest of the three, tends to get squeezed out of the picture. As a surface landmark, it often reads as a small crease or dimple between the other two.

Now let's try placing these on one of our 1947 models...

Man, just think. This is someone's grandpa now. Notice the long, diamond shaped tendinous floor of the trapezius, which itself can often be seen clearly as a surface landmark, particularly when you're as buff as this gentleman. Notice also that the lower tip of trapezius attaches to the spinous process of the T12 vertebra. Visible bony landmarks include the lateral end of the clavicle, the acromion process, spine, medial border, and inferior angle of the scapula,  and the iliac crest.

The muscles shown in the previous diagram are all shown bilaterally in this image. So we can see the larger muscles with their triangular window on both sides, as well as the posterior scapula muscles peeking through. Notice that the latissimus dorsi overlaps teres major a little bit. Keep in mind, though, that it does not obscure teres major, because it's so thin. If you're unable to locate the muscle windows in the above image, take a look at this:

In this image, only the muscle window has been given a color overlay. Infraspinatus, teres minor, and teres major peek through this window.

The blue area indicates the window formed by deltoid, trapezius, and latissimus dorsi. It's within this window that we can see infraspinatus, teres minor, and teres major. We will look at this more closely in our next post, as well as quite a few other visible muscles that I haven't even mentioned yet. Also, there is so much variation in the appearance of back muscles that I'd like to show a lot more photos! And, after all, there are lots more 1947 nudes to peruse. See you next time.

Wednesday, January 4, 2012

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!