A Treatise on Painting/Chapter 31
Chap. XXXI.—Of the small Bones in several Joints of the human Body.
There are in the joints of the human body certain small bones, fixed in the middle of the tendons which connect several of the joints. Such are the patellas of the knees, and the joints of the shoulders, and those of the feet. They are eight in number, one at each shoulder, one at each knee, and two at each foot under the first joint of the great toe towards the heel. These grow extremely hard as a man advances in years.