(1) An analysis of one hundred x-rays of knees of children between the ages of two and one-half and six years shows an absence of the ossification center of the patella in thirty-two.
(2) Tuberculosis has a definite effect on the development of the ossification of the patella, rickets has a definite effect on the time of appearance of the ossification center, while congenital lues has no constant effect on either.
(3) In the case reported of delayed appearance of the ossification centers of the patellae, the undernutrition of the patient stands out as the most important factor.
(4) Two cases are observed with two ossification centers for the patella.