Hello! Welcome back to our study of the human skeleton.
In the last lesson, you learned how to construct the torso by understanding the dynamic relationship between the ribcage and pelvis. By mastering tilt, twist, and contrapposto, you can now build a core that feels balanced and alive. Today, we'll begin attaching the limbs to that solid foundation. Our objective is to identify and draw the major bones of the upper limbs: the humerus, radius, and ulna.
Understanding these three bones is crucial. They define the length, proportion, and fundamental motion of the arm, providing the scaffold upon which all the arm muscles will later attach.
1. The Arm's Skeletal System: An Overview
The arm consists of one bone in the upper arm and two in the forearm. Let's get acquainted with them.
You might wonder: why two bones in the forearm? This arrangement is a clever mechanical solution that allows the hand to rotate without requiring the entire arm to move from the shoulder. Let's watch a brief introduction to this concept.
Drawing Arm Bones - Anatomy for Artists
This video from Proko's anatomy series introduces the three arm bones and immediately explains the critical concept of forearm rotation.
Watch the segment from 00:41 to 01:49. Focus on understanding the terms supination (palm up, bones parallel) and pronation (palm down, bones crossed). This is the most important mechanical principle of the forearm.
As you saw, the radius rotates around a relatively fixed ulna. This is the core principle we need to keep in mind as we study each bone individually.
2. Deconstructing the Arm Bones
Just as we simplified the ribcage and pelvis into boxes, we'll simplify these bones into basic forms that are easier to draw and position in space.
The Humerus (Upper Arm)
The humerus is the longest bone of the arm. For drawing purposes, we can think of it as a simple cylinder or a slightly tapered rod.
Drawing Arm Bones - Anatomy for Artists
Let's continue with the Proko video to break down the humerus into a manageable form.
Watch from 01:49 to 03:25. Pay close attention to the simplified 'croquet mallet' shape. Also, try to find the two bumps on either side of your own elbow—these are the epicondyles, which are critical landmarks for locating the end of the humerus and the orientation of the arm.
The Ulna and Radius (Forearm)
The forearm is the more complex section. The key is to remember the relationship between the ulna and radius:
- Ulna: Stays on the pinky side of the wrist. It is wide at the elbow and tapers to be narrow at the wrist. Its main job is to form the hinge of the elbow joint.
- Radius: Stays on the thumb side of the wrist. It is narrow at the elbow and widens to form the primary joint at the wrist. Its main job is to rotate.
This opposite tapering is an efficient design. The ulna is the primary bone of the elbow joint, while the radius is the primary bone of thewrist joint.
Let's watch the rest of the main segment of the Proko video to see how these two bones are structured.
Drawing Arm Bones - Anatomy for Artists
This clip covers the individual forms and landmarks of the ulna and radius.
Watch from 03:25 to 06:43. For the ulna, take note of the olecranon (the bony point of your elbow) and the fact that you can feel the bone's edge all the way down to your wrist. For the radius, focus on its rotation and its shape being the inverse of the ulna's.
3. Key Relationships and Drawing Tips
Now that you've been introduced to the individual bones, let's focus on how they fit together. Understanding their joints and visible landmarks is the key to drawing them correctly.
A great way to simplify the arm for drawing is to think of it as two connected cylinders, just as we did with the "Robo Bean" for the torso.
Drawing Anatomy Arm｜Understand Bones, Muscles, and Motion
The article "Drawing Anatomy Arm" from Han Studio has some great visuals for simplifying the arm bones into basic geometric shapes.
Scroll down to the heading "3. Simplifying Bone Shapes" and look at the diagrams. Notice how the humerus is a simple cylinder, and the radius/ulna form a tapered cylinder. This is a very effective starting point for your drawings.
The Elbow Landmarks
The most reliable landmarks for drawing the arm are at the elbow. As you learned in the video, we have the two epicondyles on the humerus and the olecranon (elbow point) on the ulna.
- When the arm is straight, these three points form a horizontal line.
- When the arm is bent, they form a triangle.
Identifying this triangle on a reference model is one of the fastest ways to understand the arm's orientation in 3D space.
Arm bones & arm movements – a guide for artists
The article "Arm bones & arm movements – a guide for artists" has excellent 3D diagrams that illustrate these concepts.
First, read the section "Elbow flexion and extension" to see a clear visualization of the elbow hinge and the changing triangle of landmarks. Then, read "Pronation and supination" to see how the radius pivots around the ulna. The GIFs in this article are particularly helpful.
4. Practice Exercise: Building the Arm
It's time to put this knowledge into practice. Your task is to act like a "human x-ray machine" and draw the skeletal structure of the arm on top of reference photos.
Estimated Time: 20-25 minutes
Tools: Your iPad and Procreate.
Instructions:
- Find 3-5 Reference Photos: Find clear photos of arms in different positions. Include examples of:
- A straight arm (supinated, palm forward)
- A bent arm (like someone flexing their bicep)
- A pronated arm (palm facing down or back)
You can use the Proko poses library, search on Pinterest, or take photos of your own arm.
- Create a New Layer: In Procreate, import a reference photo and create a new layer on top of it.
- Draw the Bones:
- Locate Landmarks: Start by trying to find the key bony landmarks: the point of the shoulder, the two epicondyles at the elbow, and the bony bumps at the wrist (the head of the ulna on the pinky side).
- Draw the Humerus: Draw a cylinder representing the humerus, connecting the shoulder to the elbow epicondyles.
- Draw the Ulna and Radius: Based on the hand's rotation (pronated or supinated), draw the ulna and radius. Remember their opposite tapering. If the arm is supinated, they will be parallel. If pronated, the radius will cross over the ulna.
- Focus on capturing the simplified forms, their lengths, and their relationship to one another.
Your goal isn't a detailed anatomical chart, but a clear structural drawing that shows you understand the components and their mechanics.
Conclusion
Excellent work today. You've broken down the structure of the arm into its three core components: the humerus, radius, and ulna. By understanding how these bones are shaped and how they articulate—especially the clever rotation of the radius around the ulna—you've built a foundational model that will be indispensable when we start adding muscles.
Key Takeaways:
- The upper arm has one bone: the humerus.
- The forearm has two bones: the ulna (pinky side) and the radius (thumb side).
- Supination is palm-up (bones parallel); Pronation is palm-down (radius crosses ulna).
- The ulna is thick at the elbow (forming a hinge joint), while the radius is thick at the wrist.
- The epicondyles and olecranon form a landmark triangle at the elbow that reveals the arm's orientation.
In our next lesson, we will continue our tour of the skeleton by moving to the lower body. You'll learn to identify and draw the major bones of the lower limbs: the femur, tibia, and fibula. You'll find that many of the principles—a single upper bone and two lower bones—are similar to the arm.