Developmental Horizons in Human Embryos: Age Groups XI to XXIII is a book written by George Linius Streeter that explores the developmental stages of human embryos from the 28th day of gestation to the 56th day. The book is a comprehensive guide to the embryonic development of various organs and systems such as the nervous system, cardiovascular system, and digestive system. Streeter's research and observations are based on a collection of human embryos that were obtained from legal abortions and miscarriages. The book is divided into 23 age groups, each representing a specific developmental stage, and includes detailed illustrations and descriptions of the embryonic structures and changes that occur during each stage. The book is a valuable resource for medical professionals, researchers, and students who are interested in the development of human embryos. It provides a detailed understanding of the complex processes that occur during embryonic development and the formation of various organs and systems. Overall, Developmental Horizons in Human Embryos: Age Groups XI to XXIII is a highly informative and comprehensive guide to the developmental stages of human embryos, written by an expert in the field.Contributions To Embryology, No. 197-230.This scarce antiquarian book is a facsimile reprint of the old original and may contain some imperfections such as library marks and notations. Because we believe this work is culturally important, we have made it available as part of our commitment for protecting, preserving, and promoting the world's literature in affordable, high quality, modern editions, that are true to their original work.