Hello, my name is Stan Prokopenko, welcome to another episode of Proko. In the previous
episode, we learned the anatomical structure of Pecs. Now, let’s take a look at how you
can apply all this information to construct the forms of the pecs in your drawings.
The pecs make a flat front plane that faces slightly upwards. The bottom plane starts
at or just below the nipple. The depth of this bottom plane determines how thick the
muscle is.
Alright, let’s do a drawing of the pecs. I’ll start with a light layin of the skeleton
to help me place the muscle on top.
Let’s start with the clavicular portion. Originating from the clavicle and stretches
the farthest of the 3 portions, until it’s covered by the deltoid.
Then the sternal portion, from the entire length of the sternum, converges toward the
armpit and dips under the clavicular portion.
The lateral border curves up toward the arm. There might even be a double curve when the
arm is abducted away from the body, because of how the sternal and abdominal sections
overlap and attach to the tendon, as you can see here. When the arm raises the muscle mass
keeps its thickness near the armpit where it attaches to the tendon. More of the stretching
happens here, closer to the sternum. The tendon from the sternal section can extend an inch
or two from the armpit and when a muscular figure flexes, it often creates a dimple,
as the muscle fibers take a sharp turn inward.
The lower border of the pecs lines up with the bottom of the sternum. According to Loomis,
the nipples are roughly one head measurement down from the chin, so the bottom of the pecs
are just below that. It’s straight and horizontal, maybe leaning a bit down laterally. When drawing
a torso that’s tilted toward you or away from you, this lower border acts as a natural
cross-contour line. Use it to show the round form of the rib cage!
In male figures, there’s a crescent-shaped fat pad on the lower outer corner that contributes
to its boxy-ness. Man boobs are simply a result of that crescent-shaped fat pad gaining more
and more mass and running over onto the rib cage. When the arm is raised, the lower mass
of the pec thins, and the lower border becomes harder to distinguish. You might see ribs
you couldn’t see before.
In the next episode, we’ll explore the female chest, and how it’s different and similar
to the male chest.
Variation (Premium Ad)
There are variations to the chest depending on the physique of the person, such as lean,
average, muscular, and heavy. To learn more about these variations, head on over to the
proko.com/anatomy. The premium section has longer lessons, 3d models, and additional
demonstrations. Just sayin’. It’s proko.com/anatomy.
Assignment
Your homework is a two-parter. For part 1, do a tracing over a model photo of the pectoralis
major and all of its bundles. If you’re not sure how to do a tracing, refer back to
the “How to do an Anatomy Tracing” lesson. For part 2 of the assignment, invent the pectoralis
major on top of photos of Skelly. I’ve provided reference photos for part 1 and 2 in the link
below. Download those and start drawing! If you have the Skelly app, you can create your
own pose and draw the pecs on top. Post your work in our anatomy group at proko.com/groups!
Credits
Thanks for watching everybody! Do the chest-bump-worthy thing and share this video with your friends,
give me a thumbs up and comment below. And if you want all the Proko news, look no further
than the Proko newsletter! Alright, see you next time!