The purpose of the present study was to clarify the fundamental histological changes in endochondral ossification and their morphogenesis in 190 infants with various kinds of diseases ranging in ages from birth to 14 months and in 3 aborted fetuses. Histopathological examination was performed on the epiphyseal plate and its precursor, that is, the diaphyseal growing part of the cartilaginous epiphysis at the lower end of the femur. Before the development of the secondary ossification center, the diaphyseal growing part showed a less distinct zonal differentiation in structure. With the progressive development of the secondary ossification center, the epiphyseal plate became well differentiated and showed a typical zonal differentiation. The cluster pattern of the proliferating cartilage cells was characteristic in the fetal life. There was a close relationship between the cluster pattern and the insufficient development of the secondary ossification center. The present study revealed that the cluster pattern, disturbances in the proliferation of the cartilage cells and calcification of the cartilage were most fundamental and influential in morphogenesis of the histological changes in the endochondral ossification in the younger infants.

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The first case in Japan of ectopic solid thymus gland of the neck in a 2-month-old boy is presented. Reports of cases of ectopic thymic tissue or thymoma in Japan are reviewed. According to Patten’s Human Embryology, the thymic primordia in man appear late in the sixth week of gestation as ventral out-growths of the third pharyngeal pouches. By the early part of the seventh week, the primordia have considerably elongated but are still connected with the pharyngeal pouches and remain associated with the pair of parathyroid glands derived from the third pharyngeal pouches. During the seventh week, they increase rapidly in mass and their distal tips begin to approach each other as they swing toward the midline just caudal to the thyroid primordium. By the middle of the eighth week the distal tips of the thymic primordia have made contact with each other and have started to descend under the sternum into the mediastinum where they lie in contact with the parietal pericardium. At any portion along this path of descent the entire gland or portions thereof may be left behind. Glimour 1), in 1941, reported 13 cases showing thymic tissue of unusual portions. Eleven of these were infants. In one there was unilateral hyperplasia with complete absence of descent from the neck. Since Hyde et al. reported, in 1944, the removal of a cystic thymus gland weighing 36g from the right side of the neck, 46 cases of incompletely descended ectopic thymus tissue in the neck have been documented in the English medical literature as described by Hinds et al.2) Because of the rare occurrence of solid ectopic thymus gland of the neck, it was felt that the first case in Japan should be added to world medical literature.

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Examinations on causal factors for interdental spaces in the deciduous canine regions were made mainly by the twin method. Observations on the interdental space and dental arch at the age of 4 years: It was found that (1) the source for variation in the size of precanine space was due to the tooth size and dental arch size, and that of postcanine space was due to the tooth size, and that (2) genetic factors were small for variation in interdental space, though genetic factors were large for variations in tooth size and dental arch size. These results possibly suggest that genetic factors for variation in tooth size and dental arch size are independent and would be regarded as being a part of environmental factors for variation in interdental space.

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A reversible hydrocolloid impression material was evaluated by testing the fine line reproducibility, SUI face hardness and dimensional changes of resultant models and also the linear shrinkage of the setting material. It could fully reproduce the 20-micron wide line on the model. The model surface was harder than that from the alginate impressions. Its linear shrinkage when cooled to room temperature was as great as 0.6% and so the impression held in the trays produced models of increased outside dimension and decreased inside dimension. The outside-inside difference was exaggerated by ice water cooling of the impressions.

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