Growth in length of the long bones in man and animals is caused by a purposeful multiplication of cartilage cells of the epiphysial cartilage plates. It is held that in the vertebrae of man the center grows within itself until it occupies the entire cartilaginous area free to it and there is not the characteristic columnar formation of cartilage cells. The epiphysis is therefore not a growth body but an organ of fixation concerned with the architecture of the spine. It is even claimed that in animals, in spite of the fact that the epiphysis is a complete disk, it does not share in the process of longitudinal growth.
The importance of this problem warranted further study of the growth of the vertebrae of animals. On gross examination of a vertebra of a dog a cartilage plate is found at each end. The microscopic appearance of this plate is similar