Posture and chest muscle development

Body: 

Something I’ve been meaning to ask:

My upper chest has developed a cushioning padding and my chest looks to have more lift. I have attributed this to muscle development from posture work.

But I also have a slight thickening, running vertically exactly mid-sternum. It can’t be seen but I can feel it. I was hoping this was also related to posture work? Maybe a small muscle developed there? I do pull my chest up many, many times a day as I find myself losing posture. And I do chest raises as part of exercise.

The thickening is not in a place that is checked during breast exams. I’m probably just
over-worrying. I thought it best to ask. Thanks, Kit

my chest does have more lift since beginning the posture, but its not muscle. its posture. I don't have any increased muscle bulk in the pectorals, and I'm all bone over the sternum.
the muscles there aren't really active when I'm in wholewoman posture, unless I'm doing something that specifically calls on them.

what are chest raises?