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Post from comictool.blogspot.com: Upper Arms, Kirby Dots

comicreference:

May 3, 2009

This week: Upper arms and Kirby dots

Drawing from life is an invaluable way to learn about the figure, and especially about variations between different people’s bodies. But if you don’t know the underlying anatomy, sometimes it can be pretty darn difficult to tell what’s going on under there, even on very well-defined models.

Nowhere else have I had this problem so badly as in the arms, and the way those muscles are layered. Yes, like everyone else I could see that the bicep bulges in the middle of the arm and pulls on something below the elbow. Yeah, I could see the pectoral pulls sideways on the humerus somewhere, and the deltoid pulls up on it from somewhere on the shoulder. But the beginnings and ends of some of these muscles are hidden, and my observations of the model actually led me to some pretty severe misunderstandings about how these muscles were arranged, which made things difficult whenever I’d try to draw these muscles from my head.

For instance, take the bicep. I figured it looked kind of like the pistons on the terminator,

attaching somewhere on my humerus and pulling somewhere on my lower arm. It bulges out where the pectoral seems to go in, so I figured the pectoral went under it. But when I’d draw it it never looked right. I was all confused.

So let’s clear all this upper arm muscle business up, and sort out what goes over what.

(click the image to see it large. I recommend opening it in a new window so you can look back and forth between it and the text.)

The dots you see in the drawing above indicate the origins and attachment points for the bicep and tricep muscles. I’ll start with the bicep side:

The bicep originates at two points on the shoulder blade, and as you can see one of the heads curls up over the top of the humerus. The bicep attaches to your radius, which is the bone that rotates around your ulna and allows you to rotate your hand up and down. I’ve shown it twisted here to illustrate just that.

The bicep is covered at the top by two muscles, the pectoral and the deltoid. The pectoral muscle crosses over the bicep completely and attaches to the humerus. The front head of the deltoid that comes off the collarbone sweeps over the tippy-top of the bicep and attaches to the humerus about halfway down. Unlike the “Terminator” conception of the bicep I used to have, the bicep doesn’t go straight up and down along the arm, but rather makes a diagonal curve from the shoulder, under the pectoral and down the the ulna on the outside of the arm.

The tricep, on the other hand, actually covers a muscle, the latissimus dorsi. (It actually covers more than that, but I’m sticking to the muscles I’ve taught you.) Latissimus inserts onto the humerus. Tricep originates on the humerus and from a point on the shoulder blade, indicated by the dots in the drawing. Tricep then inserts on the back of the ulna, the stationary bone of your forearm that forms the lower part of the elbow joint.

The back portion of deltoid covers the top of the triceps.

Oh, by the way, tool tip: To make nice, round dots in a comic, you can use a q-tip. Use the whole end, or for smaller dots,

cut off one end and clean up the edge.
This is actually how Jack Kirby made his famous “cosmic energy” Kirby dots.

Filed under tutorials Arm Arms Kirby Dots Anatomy