TEXT-BOOK OF EMBRYOLOGY 



INTRODUCTION 



The study of human embryology deals with the development of the individual 

 from the origin of the germ-cells to the adult condition. To the medical student 

 human embryology is of primary importance because it affords a comprehensive 

 understanding of gross anatomy. It is on this account that only recently a 

 prominent surgeon has recommended a thorough study of embryology as one of 

 the foundation stones of surgical training. Embryology not only throws light 

 on the normal anatomy of the adult, but it also explains the occurrence of many 

 anomalies, and the origin of certain pathological changes in the tissues. From 

 the theoretical side, embryology is the key with which we may unlock the secrets 

 of heredity, of the determination of sex and, in part, of organic evolution. 



There is unfortunately a view current among graduates in medicine that the 

 field of embryology has been fully reaped and gleaned of its harvest. On the 

 contrary, much productive ground is as yet unworked, and all well-preserved 

 human embryos are of value to the investigator. An institute of embryology 

 for the purpose of collecting, preserving and studying human embryos has re- 

 cently been established by Professor F. P. Mall of the- Johns Hopkins Medical 

 School. Aborted embryos and those obtained by operation in case of either normal 

 or ectopic pregnancies should always be saved and preserved by immersing them intact 

 in 10 per cent, formalin or Zenker's fluid. 



The science of embryology is a comparatively new one, originating with the 

 use of the compound microscope and developing with the improvement of micro- 

 scopical technique. Chick embryos had been studied by Malpighi and Harvey 

 previous to Leeuwenhoek's report of the discovery of the spermatozoon by 

 Dr. Ham in 1677. At this period it was believed that the spermatozoa were both 

 male and female and developed in the ovum of the mother; that the various parts 

 of the adult body were preformed in the sperm-cell. Dalenpatius (1699) believed 

 that he had observed a minute human form in the spermatozoon. Previous to 

 this period, many animals were believed to be spontaneously generated from slime 

 and decaying matter as asserted by Aristotle. The preformation theory was first 

 combated by Wolff (1759) who saw that the early chick embryo was differentiated 



