Scientia Sinica

No. 1 WOO: OSSIFICATION « GROWTH OF HUMAN ZYGOMATIC BONE 135

The ossification centre of the zygomatic bone appears first as a small angular point located in the lower outer side of the orbit. In a fetus of 37 mm C-R length, estimated at about 61 days, the anterior or infra-orbital and posterior or zygomatic processes are seen to be formed. In a fetus of 42 mm CR length, estimated at 64 days, the infra-orbital and zygomatic processes are more marked and the fronto-sphenoidal process begins to appear (fig. 2). The orbital process appears in a fetus of 53 mm C-R length, estimated at 71 days (fig. 3). Then the zygomatic bone possesses all its characteristic features.

SUMMARY

1. The zygomatic bone of man is ossified from one centre only which appears in a fetus of eight and a half weeks old.

2. The infra-orbital and zygomatic processes appear at the end of the 8th week of the fetus.

3. The infra-orbital and zygomatic processes are more marked and the fronto-sphenoidal process begins to be differentiated in the 9th week of the fetus.

4. The orbital process appears in the 10th week of the fetus and then the form of the zygomatic bone is completed.

REFERENCES . [1] Dawson, A., 1926. A Note on the Staining of the Skeleton of Cleared Specimens with Alizarin Red S. Stain Techn., 1, 123—124. [2] Gray, 1948. Anatomy of thé Human Body, Twenty-fifth ed., edited by Charles Mayo Goss, Lea & Febiger, Philadelphia, 168—170. [3] Hollister, G., 1934. Clearing and Dyeing Fish for Bone Study, Zoologica, 12, §9—101. [4] Lundvall, H., 1905. Weiteres ueber Demonstration embryonaler Skelette. Anat. Anz., 27, 520—523. [5] Mall, F. P., 1906. On Ossification Centres in Human Embryos Less than 100 Days Old. Am. J. Anat., 5, 433—458.

[6] Morris, 1942. Human Anatomy, Tenth ed., edited by J. Parsons Schaeffer, The Blakiston Co., Philadelphia, 164—165.

[7] Noback, Charles R., and Eleanor Noback, 1944. Demonstrating the Osseous Skeleton of Human Embryos and Fetuses, Stain Techn., 19, 51—54.

[8] Patten, B. M., 1946. Human Embryology, The Blakiston Co., Philadelphia,

[9] Rambaud, A., and Renault, Ch., 1864. Origine et développement des os. Paris. [10] Schultze, O., 1897. Ueber Herstellung und Conservirung durchsichtiger Embryonen zum Studium der Skeletbildung. Verh. Anat. Ges., 11 Versam., 3—5.

[11] Spalteholz, W., 1914. Ueber das Durchsichtigmachen von menschlichen und tterischen Praeparaten, 2. Auf., Leipzig.

[12] Woo, Ju-Kang, 1949. Ossification and Growth of the Human Maxilla, Premaxilla and Palate Bone, Anat, Rec., 105, 737—761.