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It is known that, in addition to their presence in the periodontal ligament, the existence of oxytalan fibers can be shown in other tissue structures as well. No unanimous opinion concerning the function of these fibers can be found in the literature. Pre-elastic fibers are also stained when one tries to demonstrate oxytalan fibers according to Fullmer's technique; confusion has to be eliminated. In the first instance, in our experiments we could observe the presence of oxytalan fibers within the temporomandibular joints of Wistar rats. Next the reaction of these fibers was studied under experimental circumstances by carefully removing all molar crowns; as a consequence, more stress to the joint was induced. By sectioning the mandibular joint and adnexa in the vertical and sagittal plane, we obtained a three-dimensional image. The sections were also stained according to a modified staining method of Fullmer and the elastin staining technique of Gieson/Hart. The molar crowns of ten rats at the age of 2 months and ten rats aged 4 months were removed. The control animals matched the experimental rats in number and age. After 1 month all rats were decapitated. In the nearly cell-free central zone of the articular disk, where, under normal and experimental circumstances, only very few elastic fibers can be found, the number of oxytalan fibers in the experimental animals increased 40 percent with respect to the controls. These findings suggest that the augmented number of the involved fibers functions as a kind of resistance against distortion.

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The coronal suture with the adnexa was excised in 1-week-old rats and replanted onto the exposed dura mater of the same rat. After replantation, the original internal part of the suture (= pars interna) was located on the external surface of the cranial vault, while the original external part (= pars externa) was located on the dura mater. The animals were sacrificed 1, 2, 3, 4, 5, 6 and 7 weeks after operation. The microscopic observations, done 3, 4, 5, 6 and 7 weeks after replantations, reveal that gradually such alterations occur in the replanted suture that the pars interna transforms into a pars externa and vice versa. These modifications are discussed in the light of the general articulations of the cranial bones. In the observed alterations of the replanted coronal suture we see a confirmation of the hinge hypothesis proposed by Oudhof.

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The aim of the present study was to determine the presence of alkaline phosphatase during various stages in development and closure of the sutura interfrontalis. The histological sections reveal that this enzyme could primarily be demonstrated in the dura mater of this suture. In further developmental stages, alkaline phosphatase could be observed within the intermediate zone as well as the pericranium. These findings are brought in relation with the occurrence of synostosis which can be induced under experimental conditions.

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From fetal rat skulls, tissue containing the 19-day-old presumptive coronal suture was excised and transplanted onto the exposed dura mater of adult rats. Host animals were sacrificed after 1, 2, 3, 4, 5 and 6 days. From the results of these experiments, the following conclusions can be drawn: (1) in all transplants chondrogenic activity occurred, resulting in the production of ectopic cartilage, and (2) cartilage development only starts on the cerebral side of the transplanted embryonic dura mater just beneath the area of the presumptive suture. Transplanted presumptive sutures of 21-day-old rats do not produce cartilage. The findings suggest that the suture undergoes a process of maturation. The existence of an osteogenesis-inhibiting mechanism, located in embryonic sutural tissue and being transmitted to the developing dura, is discussed.

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The purpose of the present study was to determine the presence of alkaline phosphatase within the coronal suture, the dura mater and the pericranium. The histologic sections reveal that no alkaline phosphatase activity could be observed within the coronal suture as well as the dura mater, while the pericranium did contain this enzyme. These findings are brought in relation with the occurrence of synostoses, which can be induced under experimental conditions.

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Histological examination of skulls of 3- to 7-month-old human fetuses reveals in the fourth month of fetal life the development of a morphologically distinctive tissue in the area between the frontal and parietal bones. In this particular area, the pericranium tends to bulge outward while the dura mater shows the same in an inward direction. Consequently, a spindle-shaped blastema is enclosed. This spindle-like structure is only temporarily present; by about the sixth month of fetal life it has disappeared. Secondly, it was observed that prior to the development of this blastema mainly undifferentiated mesenchymal cells and only few fibroblasts are present in the area between the approaching ossification centres. In the full-grown blastema both types of cells are present in about equal numbers. However, once the blastema has been formed, fibroblasts predominate over mesenchymal cells. This tissue structure is also clearly distinguishable in the developing fetal rat skull. In this species, however, the spindle-shaped blastema appears at a later phase of fetal development, i.e. at about the 20th day. In both species, man and rat, the temporary presence of this blastema is not confined to the presumptive coronal suture only, but is demonstrable as well in other cranial sutures.

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