Bursæ over both malleoli.
Well-formed bursa under tendo achillis.
Macacus Rhoesus L.
This specimen showed more examples of bursæ than the two of Cercopithecus.
Bursæ present over styloid processes of ulna and radius, also over metacarpo-phalangeal joints.
Bursa well-marked over malleoli and under tendo achillis.
Bursæ present over metacarpo-phalangeal and metatarso-phalangeal joints.
No bursæ over phalangeal joints.
Further Undesigned Experiments.
The preceding facts as to the natural history of bursæ in man and some lower Primates, even if they stood alone, are enough to produce conviction as to the manner in which bursæ of all degrees of perfection are formed by function, and point to the origin of the initial stages of these structures. But they do not stand alone, for in man there have been carried out certain undesigned experiments in a similar direction, comparable to those described in the sections on direction of hair and arrangement of papillary ridges. These demonstrate the fact that frequent friction of skin over a hard surface has the power of producing adventitious bursæ in regions where they are not found in the normal state.