The muscle placement on models looks mostly good, however the area on the back of the shoulder / armpit seems to be a bit off, the latisimus dorsi and the teresmajor make up the shape of the rear of the armpit, and their attachments are kind of weird, but important for drawing that part of the body properly .
This website has a good illustration and has specifics on the attachment points.
https://www.getbodysmart.com/arm-muscles/infraspinatus-muscle
The Lattisimus dorsi, pectoralis major, and teres major all attach at the same place oddly enough, medical anatomy refers to it as "The lady between 2 majors" You can start to see how those 3 muscles all attach by looking here.
https://www.getbodysmart.com/arm-muscles/pectoralis-major-muscle, they all attach at that same point on the humerus, the bicipital groove.
I hope this helps. I also love the skeletons lifelike face.