One hundred and eighty-four human embryos and foetuses were studied. They ranged from seven to 460 millimeters in length.
The skeleton of the foot was blastemal by Stage 17, and the various elements began to chondrify between Stages 18 and 23, that is, from approximately five and a half to seven weeks after ovulation. Chondrification occurred in a definite sequence.
Cartilage canals were first seen at forty-three millimeters; they were found in all skeletal elements, including sesamoids. Their first appearance occurred in a definite sequence.
Ossification was first noted in the metatarsals and distal phalanges early in the fetal period, and later in the proximal and middle phalanges. Some middle phalanges had not begun to ossify at term. Periosteal ossification was first noted in the calcaneus at ninety-three millimeters, and endochondral ossification at 150 millimeters (about five months). Endochondral ossification was first noted in the talus at 253 millimeters (about eight months). In two specimens at term, endochondral ossification was beginning in the cuboid. Cartilaginous sesamoids were first noted at thirty millimeters; their distribution and frequeney during the fetal period roughly corresponded to those reported for the adult.
Fusions were noted as follows: talocalcanean, calcaneonavicular, cuneometatarsal, and interphalangeal. Fusion of the middle and distal phalanges of the little toe was common. Accessory ossicles. that were noted included os paracuneiforme, os intermetatarsale, and a separate cartilage in the tendon of the tibialis posterior.
Homogeneous interzones were present in the joints of the foot by Stages 20 to 21. Cavitation began in a few joints during the embryonic period, but the formation of three-layered interzones, followed by cavitation, began in most joints during the early fetal period.
Capsules and ligaments were present as cellular condensations before cavities and, in sonme cases, before three-layered interzones appeared.
Copyright 1959 by The Journal of Bone and Joint Surgery, Incorporated