The study of prenatal development provides many clues for understanding the physiology as well as the pathogeny of malformations and many diseases. I became interested in the analysis of human development as a young medical student more than 30 years ago, and I have stayed in this field all my life. In my studies, I always tried to compare the events of different disciplines such as genetics, anatomy, bio chemistry and physiology. I learned that the development of a structure is, under normal circumstances, strictly determined and that the development of structures always precedes their proper function. There are no changes in function without changes in structure. The life of every cell is genetically preprogrammed and the program may be modified by complicated interactions with environment. Recent progress in our knowledge is basicly related to technology. However, using all the tools of today's technology, we are still unable to understand the basic normal development. After almost thirty years of work, I am trying to present a subjective review of the development of the human endocrine glands. I am presenting an image emerging from my experience. I personally studied several hundred human embryos using mostly anatomical, histochemical and some biochemical techniques. I found much additional information in the literature."

A little picture is worth a million words. Chinese proverb Prenatal human development is an extremely complicated process related to genetics, biochemistry, anatomy, and physiology. There are no developmental changes, either chemical or morphologic, without simultaneous changes in molecular organization. The astonishing buildup ofbiostructures always precedes their proper function. The development of an embryo is genetically coded and is based on interactions related to the selective switching on and off of genes. Interactions are cell-to-cell mediated, mediated by extracellular fluids, or mediated by special pathways. Every substance involved in developmental is to be recognized by its target. interactions, before triggering a metabolic or a morphogenic event, Complex physical and immunologic recognitions are involved in the process of differentiation. Small pieces of evidence are collected to create a mosaic picture elucidating the development. This picture is fascinating and represents the biggest biological puzzle: the puzzle of development. There is no doubt that analysis of human prenatal development is a basis for understanding normal and pathologic relationships between structure and function. Today, there are approximately 2000 different inborn congenital anomalies and syndromes. This book attempts to present a complete realistic account of human morphogenesis, the differentiation of structures, using direct photographs of normal specimens obtained from legal medical abortions of unwanted pregnancies. Emphasis has been placed on contemporary techniques: histochemistry and scanning electron microscopy. The text is as simple as possible; meticulous detailed anatomic descriptions have been omitted.