Narrow jaw - what can be done to make my face, the lower half in particular, less narrow and more normal? (Photo)

your perspective is quite accurate. You have a 'high angle' growth pattern which yields a short 'ramus/back of the jawline' and a 'longer ' section of the lower jaw which gives the face a tapered 'triangular' shape. The 'improvement' can be nicely achieved with augmentation of the angles/ramus of the jaw which increases the height at the back of the jaw; and increases the width of the jaw. It should be combined with a genioplasty in some cases to ensure a smooth contour between the front and the back of the jawline. This is a common growth pattern often associated with a malocclusion as well.