Most embryologists will say after Thoma, that bloodvessels follow the pattern set by organs and have no influence on organs in themselves. If this be true in normal development, what would we find in abnormality? If there be a certain vascular pattern in the developing face, will this pattern be essentially different in cases of clefts of primary and secondary palate? Or is Thomas statement also true here, and are the differences due to following the abnormal formation of the nasal and maxillary parts of the face? Could it be so that the unknown agents responsible for abnormal development act in a time of change in vascular pattern, take their chance just when there is a depletion in vascular supply? Or to the contrary, is there a specific vascular pattern which would allow causal haemato genic agents to reach the areas where we find abnormal development? To answer these questions we will have to compare vascularpatternsinnormal embryos and those with clefts, in stages as near as possible those in which the formation of the clefts takes place, which means for the primary palate the 9-12 mm. stage, for the secondary palate about the 35 mm. stage (Streeters Groups XV-XVII and XXI). Our research concerns normal embryos of 8, 11. 5, 12, 15, 17, 18, 25, 29, 30, 34, 35, 40 and 50 mm.

Inhalt
Formation and Growth of Vessels and Vascular Patterns.- The Vascular Pattern and its Changes During Development of the Primary and Secondary Palate in Normal Embryos of 850mm..- Description of the Facial Region of six Embryos with Clefts in Primary and Secondary Palate and of the Vascular Pattern Therein, Followed by a Comparison with Patterns in Normal Embryos of the Same Stage.- 1. Zürich Embryo 13mm..- 2. Heidelberg Embryo Scha 22mm..- 3. New York Embryo 36mm..- 4. New York Embryo 46mm..- 5. New York Embryo 48mm..- 4. Zürich Embryo 64mm..- The Changes in Vascular Pattern During Development of Cleft Primary and Secondary Palate in Embryos of 1364mm.- Discussion.- Summary.- References.