Today I would like to walk you through another insight. Nowadays thanks to new technologies and more powerful machines, we are able to create and simulate digital muscle systems in a more accurate way and to be more close to a real anatomical structure.
One of my favorite muscle is for sure the Coracobrachialis, is not one of the most acclaimed muscle, like the pectoralis major, the biceps or the trapezius but, if properly set up, it will give a sensible plus to your Muscle Body rig. Let's see why!
Studying properly the origins, the insertions and the placing of your digital muscles is the key for having a solid BodyRig.
The coracobrachialis has the following origin and Insertion point: Coracoid process of the scapula and Mid-medial surface of the humerus.
Whether you're binding or solving the skin of your character, the armpit area is one of the most complicated one.
We have multiple sets of muscles that cross and define this section, the coraco is one of the "helper muscle" that will allow you to achieve and to read easily the deformation of this area.
Let's have a look to some references:
From those pictures you can clearly see that the Coracobrachialis is giving you a more amplified sensation of connectivity between arm and chest.
One common mistake that students make (I made it as well) is to create slightly bigger biceps that cover and consolidate a bit more this area, without implementing the Coraco.
The reason of this mistake, is related to the origin of the biceps-short-head, it's in the same area (but not the same spot) of the coracobrachialis (Coracoid process of the scapula, as you can see from the following picture) .
Let's keep in mind that a bigger biceps-short-head will never give you the nice straight line of the coracobrachialis because of the different insertion points.
In conclusion, don't be worried to spare time studying muscles' origins and insertions, I'm sure you will save a lot when the entire Muscle system is in place and you will have to set the general behavior ;)
A more peculiar advice on the coracobrachialis itself: try always to find enough space between Lattissimus Dorsi and biceps to shape the coraco properly. if you are struggling to find space try to reduce a bit the volume of the top part of the biceps, there is the transition of the tendon area that give you the freedom to reduce the volume without issues.
I really hope this insight helped you to improve a bit and thanks for your time!