Paper - A Human Embryo Twenty-Six Days Old

Introduction

SEVERAL years ago Dr. C. 0. Miller of the Johns Hopkins University gave me a very young human embryo which was so well preserved and so perfect in all respects that it justified a very careful study. He very kindly has procured for me the following history.

‘‘The woman, twenty-nine years old, had been married nine years, and had always menstruated regularly every twenty-eight days, the period each time lasting three days. She had given birth to four healthy children, the last having been born January I, 1888. Her last menstrual period began on October 6, 1888, and ended on the 9th. Her next menstrual period should have begun on November 3, but on account of its falling out, she concluded that she was pregnant, and, on November 20,began taking large doses of ergot, which she had repeatedly taken to produce abortion in earlier pregnancies, but with no result, Several days later she applied to a professional abortionist who used instruments, after which she had a continuous metrorrhagia, and called for me to attend her. On November 27, just fifty-two days after the beginning of the last menstrual period, the unbroken ovum came away. It was kept in a cool place for three hours, and then without opening placed in eighty per cent alcohol.”

When the specimen came into my hands it was found covered with villi two or three millimetres in length, without which it measured 22 mm. in diameter. Upon opening it I found that the embryo had been hardened without any irregular shrinkage. A year later it was shown by staining a portion of the membranes that the cells were preserved excellently; and the embryo was then stained with alum carmine, imbedded in paraffin, and cut into sections at right angles to the branchial arches 15 microns thick.

Age

The nape-breech length measured 7 mm. and the vertex- breech 6 mm. The study of mammalian embryos, as well as a series of human embryos, tells us that this embryo cannot be over a month old. From the results of post-mortem examinations of women shortly before the' beginning of menstruation, Bischoff, Williams, Dalton, Leopold, and others place ovulation two or three days before the beginning of menstruation.' Espe- cially on account of the study of several cases in which the earliest possible cohabitation took place a week or two after the last menstrual period, embryologists and gynecologists reckon the duration of pregnancy from the beginning of the first period which has fallen out.

So in order to estimate more accurately the age of this em- bryo, we must subtract twenty-eight from the time which has elapsed since the beginning of the last period (fifty-two days), and add two for the time between ovulation and menstruation. The shape and size of this embryo correspond with that described by others as the fourth week, and twenty-six days is in all proba- bility its age.

External Form

The embryo is flexed upon itself, forming almost a circle (Pl. XXIX., Fig. I). The head shows the outline of the brain within, and also a marked elevation over the region of the Gasserian ganglion. The nasal pit is a large shallow depression, being well exposed on both sides. T h e lense is small, and is surrounded by a groove which is continued between the superior maxillary process and nasal pit.

Three branchial arches are visible on the right side, and four on the left. The ventral end of the first is bulbous, while from its dorsal end the superior maxillary process arises. The second is also bulbous on its ventral end, the major portion of the trunk hanging over the third arch. This is the embryonic operculum which will finally close the sinus praecervicalis. The third arch lies more towards the median line, that is, it is within the sinus praecervicalis. The fourth arch is visible only