Flanks

The horse's flanks are hurt.

Cover the flanks!

One of these strangers was about forty years of age, tall, and thin in the flanks, with an aquiline nose, dark penetrating eyes, and a shrewd but sinister cast of countenance.

Sherry's mother had taught her to start grooming her horse by brushing its flanks.

The horse was so thin, I could feel its bones through its flanks.