The Ethics of Medical Homicide and Mutilation

by Austin O'Malley

2. An albuminous fluid collects within the morula, and thus the Vesicle or Blastocyst is formed. The blastocyst is called more commonly the Cleavage Cavity or the Segmentation Cavity. As this cavity widens the cells are seen to be arranged in two groups—(a) an enveloping layer, the epiblast, from the outermost plate of which develops later the Trophoblast, or the nourishing and protecting covering of the embryo; (b) an Inner Cell Mass, made up of granular cells, attached to the epiblastic layer at the Embryonic Pole of the Vesicle. These two stages probably take place in the Fallopian tube, and thereafter the embryo is in the cavity of the uterus.

3. In the third stage the Inner Cell-Mass separates into two layers derived from the inner cell-plate of the blastula. The mass flattens and spreads peripherally, until finally it is divided into two layers. The outer is the Ectoderm and the inner is the Endoderm or Hypoblast. The three steps just described have not yet been seen in the human species by any one, but they are inferred very confidently from what is well known of the development in mammals most closely resembling man in physical formation.

4. By the conversion of the one-layered blastula into two layers of cells, the Gastrula stage of the embryo is attained. The Gastrula consists of two layers of cells surrounding a central cavity, which is the Archenteron, or the body-cavity that will hold the intestines. During the past twelve years many specimens of human gastrulas have been observed. The earliest form was that seen in 1908 by Teacher and Boyce.[35] This embryo was 1.95 mm. in length by 0.95 mm. in width, about twice the size of a pin-head. It showed on section the endoderm, the ectoderm, and the beginning mesoderm, enclosed in a spherical mass of trophoblastic cells. The mesoderm is a plate of cells lying between the endodermic and ectodermic plates. When the mesoderm develops into two plates, a cavity, called the Primitive Coelom, appears between the plates. The Coelom becomes the space between the viscera and the body-walls in later development.

From the primary embryonic layers of cells, the ectoderm, the endoderm, and mesoderm, all the parts of the body are built up. From the ectoderm are produced the skin, nails, hair, the epithelium of the sebaceous, sweat, and mammary glands, the epithelium of the mouth and salivary glands, the teeth-enamel, the epithelium of the nasal tract, of the ear, of the front of the eye, and the whole spinal cord and the brain, with their outgrowths.

From the endoderm come the epithelium of the respiratory tract, of most of the digestive tract with the liver and pancreas, the epithelium of the thyroid body, the bladder, and other minor parts.

From the mesoderm are developed bone, dentine, cartilage, lymph, blood, fibrous and alveolar tissues, muscles, all endothelial cells, as of joint-cavities, blood-vessels, the pleura and peritoneum, the spleen, kidneys and ureters, and the reproductive bodies.

The epiblast now with its mesoblastic lining begins to form the Chorion, an embryonic intrauterine appendage; and the endoderm encloses the Archenteron or primitive gut. Before the end of the second week of gestation the heart is indicated as two tubes in the mesoderm, and the blood-vessels begin to be produced in the yolk-sac. About the twelfth day the mouth-pit shows, and the gut-tract is partly separated from the yolk-sac. The medullary plate of the nervous system is laid down about the fourteenth day, and the nasal area is observable. The maternal blood escapes into spaces about the embryo enclosed by masses of embryonic cells, which have not separated from one another, but which are known collectively as Syncytium.

5. With the third week the stage of the embryo, technically so called, begins. During this week the body of the embryo is indicated. There are three layers of cells, already mentioned, the ectoderm, mesoderm, and endoderm, and these lie on the floor of the enveloping Amnion. The amnion is a loose fluid-filled sac (the caul) enveloping the fetus to protect it from jarring. The fluid in it is the "waters" that escape in parturition when the infant breaks through the caul. The archenteron in the third week shows the beginning of a division into two parts: the part that will go to the body proper of the embryo, and the part outside the body of the embryo which will form the yolk-sac, or umbilical vesicle, from which the embryo will draw sustenance until the placental vessels have been formed. The part of the archenteron that remains within the embryo proper begins in this third week to be moulded into the head-cavity. The forepart of the archenteron will later make the alimentary tract from the mouth to the middle of the duodenum, or small intestine beyond the stomach. The other part of the archenteron wall make the Allantois, the hind gut and the bladder. The allantois becomes a part of the fetal umbilical cord after the formation of the placenta.

During this third week the dorsal outline of the embryo is concave; the heart has a single cavity, which will begin to divide during the fourth week; the vitelline blood circulation begins, and the blood-vessels of the visceral arch are laid down. The digestive system is advanced to a gut-tract, which is a straight tube connected with the yolk-sac. The liver evagination is present and the oral pit is a five-sided fossa. The respiratory system is represented by the anlage of the lungs, a longitudinal protrusion of the ventral wall of the esophagus. The genito-urinary system begins as the Wolffian bodies. The mesoderm starts to segment to form the skin, and the neural canal (from which develop the spinal cord and brain) for the nervous system forms. The fourth ventricle of the brain is indicated, and the vesicles of the fore brain, mid brain, and hind brain are recognizable. The ears, nose, and eyes, muscular system, skeleton, and limbs are also beginning to be recognizable. At about the sixteenth or eighteenth day of gestation the various parts of the embryo rapidly differentiate.

In the fourth week all these parts advance. The atrium cavity of the heart begins to divide; the alimentary tract shows the pharynx and esophagus, stomach, and gut; the pancreas starts, the liver diverticulum divides, and the bile-ducts appear. The lung anlage bifurcates and the primitive trachea is seen. The ventral roots of the spinal nerves appear, the interior ear is indicated, and the eye is deeper. The buds of the legs and arms appear about the twenty-first day—by the thirty-second day even the fingers are present. The four heart-cavities are formed, the intestinal canal is nearly closed, the first indications of the liver and kidneys appear. The child now has reached the fetal stage, and its living body is made up of myriads of cells all derived from the original fertilized ovum. The fetus is then one centimetre, or two-fifths of an inch, in length—about the length of the word "fetus" here.