Its Length and Weight—It Osseous, Muscular, and Vascular Systems—The Fetal Circulation—Nervous System—Organs of Sense—Its Lungs, Heart, and other Internal Organs.
As a matter of natural science, rather than one of real practical utility, to you for whom I write these letters, I present you with a description of some of the more important characteristics of the fetus. In doing this I acknowledge myself indebted to Mr. Wilson, the distinguished anatomist before referred to.
The medium weight of a child of the full period, at birth, is seven pounds, and its length seventeen inches; the extremes of weight are four pounds and three quarters, and ten pounds; and the extremes of measurement fifteen and twenty inches. The head is of large size, and lengthened from before backward; the face small. The upper extremities are greatly developed, and the thorax expanded and full. The upper part of the abdomen is large, from the great size of the liver; the lower part is small and conical; and the lower extremities are very small in proportion to the rest of the body. The external genital organs are very large, and fully developed, and the attachment of the umbilicus is one inch farther from the vertex of the head than from the soles of the feet; and one inch farther from the ensiform cartilage than from the symphysis pubis.
OSSEOUS SYSTEM.
The development of the osseous system is treated of in the various works on anatomy. The ligamentous system presents no peculiarity deserving of remark.
MUSCULAR SYSTEM.
The muscles of the fetus at birth are large and fully formed; they are of a lighter color than those of the adult, and of softer texture. The transverse striæ on the fibers of animal life are not distinguishable until the sixth month of fetal life.
VASCULAR SYSTEM.
The circulating system presents several peculiarities: 1st. In the heart; there is a communication between the two auricles by means of the foramen ovale. 2d. In the arterial system; there is a communication between the pulmonary artery and descending aorta, by means of a large trunk, the ductus arteriosus. 3d. Also in the arterial system; the internal iliac arteries, under the name of hypogastric and umbilical, are continued from the fetus to the placenta, to which they return the blood which has circulated in the system of the fetus. 4th. In the venous system; there is a communication between the umbilical vein and the inferior vena cava, called the ductus venosus.