Original diagrams from Gray's anatomy, now out of copyright. This diagram has been reproduced from Gray's Anatomy 20th US edition which has now lapsed into the public domain
- https://commons.wikimedia.org/wiki/File:Gray182.png
- https://commons.wikimedia.org/wiki/File:Gray183.png
- https://commons.wikimedia.org/wiki/File:Gray184.png
- https://commons.wikimedia.org/wiki/File:Gray185.png