Torso drawing tutorial
Analysis from a painting
Painting by Charles Gleyre: Le coucher de Sappho (1867).
Begin by defining two ovals for the ribcage and the hips. The ribcage is usually a little bigger and longer, but feel free to modify this as you like when drawing a cartoon character or fantasy figure.
These ovals will make up the big masses of the torso. They should point at each other in the front at an angle. They should not intersect but leave some space between them for the waist.
Add vertical surface lines to the ribcage and hips oval to indicate their 3D orientation. Add a curve to the lower end of the ribcage - the bony part of the ribcage (the ribs) ends here. Mark where the head is attached to the ribcage and define the positions of the shoulders.
Connect the two big parts that make up the torso. Here you can decide on the size and shape of the figure's belly. Create a slim waist or fat bulges, as you like. Draw the navel if the torso is seen from the front. Draw the buttocks too and decide on the position of the legs/thighs).
To find the correct position of the breasts on the ribcage, start at the jugulum (the hollow at the point where the neck connects with the ribcage in the front). Draw an (imaginary or real) line over the surface of the ribcage at a 45 degree angle to either side, like an upside-down V, but in 3D, i.e. following the curve of the ribcage. You'll end up with two points that mark the location of the centers of the breasts. When drawing a child or man, this is approximately the position of the nipples. When drawing a woman or a girl post puberty, you need to add the breasts like cups or hemispheres (3D!) over these points (or a little lower (depending on the pose, due to the effect of gravity). Note that in three-quarter view, due to the roundness of the ribcage, one breast will be seen from the front (or almost so) and one breast will be seen from a profile view.