This is the sweatshirt I made named Brain Damage. It is based off of a drawing I made a few weeks prior to this. The entire thing took me about a week to make, working on it about three hours a day.

Supplies

A measuring tape or ruler.
Some form of digital software which can allow you to draw and save images as a PNG. For example, I favor Adobe Photoshop which is what I used to make this.
Access to a heat transfer vinyl printer. I go to a local store who prints my images. The entire print cost me $48.
A black sweatshirt.
Hand iron or heat press. This is what you will need to transfer the image onto the sweatshirt.

Step 1: Step 1: Finding the Dimensions of Your Sweatshirt

You will need to measure the length and width of the front and back of both arms (getting separate dimensions for the forearm and upper arm), the front and back of the torso (the length and width of the chest), and back of the hood (flatten it out and then measure). These size dimensions will determine how big you are to draw and print the images that will be pressed on.

I would recommend after measuring each length you write it down on a piece of paper because it will be very important in the next step.

Label the dimensions as follows:

Back Hood: WxH

Front Chest: WxH

Back Spine: WxH

Front Right Up Arm: WxH

Front Right Forearm: WxH

etc...

Step 2: Step 2: Begin Drawing the Bones

You will next need to open the digital art software you will be using and create a new project with the dimensions you found for your chest. Make sure it is created at 300dpi.

Now, begin drawing the ribcage you want portrayed on your sweatshirt.

After you finish drawing it, save it as a PNG file and label it "Front Chest WxH."

Do this same process with every part of the body you wish to have on the sweatshirt.

Step 3: Step 3: Print the Images

Now you will need to print the images you just created. You can do this by printing them at home on cheaper heat transfer paper (much less expensive) or by sending them to a professional company to get them printed on real heat transfer vinyl paper (what I did; cost me about $48).

(If you will be using you home printer, make sure you print on dark fabric transfer paper.)

Whichever you choose, you need to get them printed at the dimension they are named as.

Step 4: Step 4: Transferring the Images

Now you will need to get out your iron or prepare your heat press.
For my project, I used a hand iron because I didn't have a heat press at the time. However, this absolutely could be done more efficiently with a heat press.

This step is pretty self explanatory; you find the bone that you named for a specific part of the body, peal off the backing, and iron it down. You will need to hold the iron there for some time and use a little muscle.

For more specific directions on how to use the heat paper, iron, heat press, or heat vinyl, you will need to look at the manufacture's directions prior to this step.