Talk:Paper - Two choice human embryos at Streeter's horizons XI and XIV

From Embryology

Two Choice Human Embryos at Streeter’s Horizons XI and XIV


Human embryologic material in superb condition is still relatively rare. The two specimens to be presented here were obtained by hysterectomy and were fixed while still alive by opening the chorionic sacs under 10 per cent formalin. Their anatomic relations to the embryonic membranes and to the deciduas were deliberately retained.

The ventral views herein illustrated are desirable supplements to the lateral and dorsal views that are usually presented in textbooks of human embryology.“ “- 7' Four other factors contributed, however, to our decision to present ventral views: both implantations were posterior (dorsal); the capsular deciduas and chorionic sacs were opened anteriorly (ventrally); the body stalks were not severed; the specimens are being used as excellent additions to the demonstrations for a medical course in human embryology.

From the Departments of Anatomy and Obstetrics and Gynecology, University of Minnesota, Minneapolis, Minn.

Aided by grants from the National Institutes of Health (A-1244) and from the Medical Research Fund of the Graduate School of the University of Minnesota.



Mrs. L. L., a 29-year-old para 3003, had been observed for several years for recurrences of a malignant melanoma which had first appeared during her first pregnancy. A few months prior to the present pregnancy, malignant melanoma was found in a left inguinal lymph node.

Menses normally occurred every 28 days. The last menstrual period had begun on June 12 and hysterectomy was done on July 19. A rabbit test for chorionic gonadotrophin was positive prior to operation.

Membranes and Embryo

The embryonic membranes and the embryo were examined after fixation in formalin (figs. 1-3). The chorion was covered with villi, and it had a large cavity which enclosed the yolk sac, amnion, body stalk, and embryo. The dimensions of the chorion were 18 X 15 mm. The yolk sac was a spherical structure with blood islands, and its diameter was 2.5 mm. It was connected with the embryonic gut by means of a short yolk duct, which is depicted in optical section (fig. 2). The amnion, 3.1 mm. in length, was a translucent membrane.

fig. 1. Case I. In this block of endometriurn from the posterior uterine wall, the embryonic membranes and embryo have been exposed by incision of the decidua capsularis and chorion and reflection of the flap (hinged upward in drawing).

As a means of studying the surface of the embryo and, also, certain embryonic structures, the entire specimen shown in fig. 1 was rotated in a dish of formalin. Thus, the embryo was examined in all views except the dorsal; a dorsal view could not be obtained without damaging the body stalk. The embryo, 2.9 mm. in length, showed slight lordosis in the region of the yolk duct. The cephalic neuropore was a broad opening, as illustrated. The otic invaginations were widely open pits. Two branchial swellings (bars) were present, the mandibular and hyoid. The oral membrane had not ruptured. The heart was an S-shaped tube. A few mesoblastic somites could be seen, but the total number could not be observed.

Comparison with Carnegie Embryos

Even without knowing the exact number of somites, the observed features showed that the embryo was similar to a Carnegie embryo of 14

fig. 2. Case I. Ventrolateral aspect of the embryo, together with the amnion, yolk sac, and body stalk, when transilluminatecl with horizontal beams of light and viewed in the field of a dissecting microscope.

paired somites, No. 4529 (Heuser). Morpho- regarded as eligible for Streeter’s horizon XI, logically, its development was more advanced 13 t0 20 S0mil€S (StI'€€t€f“) than that in an embryo of 13 somites, No. 6344 .

(Streeterll) and less advanced than that in one Emmated Age

Of 17 80111365, N0. 5072 (AIW€11)- All 111956 The operation was done 37 days after the onobservations indicate that our embryo should be set of the last menstruation. Assuming that

fig. 3. Case l. Ventroloteral aspect of head and heart when viewed through the translucent amnion and ventral wall of the embryonic chest. Only a port of the yolk sac is shown (bottom center and right).

ovulation might have occurred at about the middle of an expected menstrual cycle of 28 days, we subtracted 14 days and arrived at an estimated ovulation age of 23 days. This estimate is in keeping with the ovulation age of embryos of horizon XI, namely 24 1- 1 days (Streeter“). In estimating the ovulation age of embryos of horizon XI, Streeter matched the 16 specimens against monkey embryos of known ovulation age; in cases in which the estimates were at variance with the menstrual history, the developmental status was given greater weight than the menstrual data.



Mrs. F. F., a 41-year-old para 2002, was found to have an adenocarcinoma of the left breast in September. In October a similar tumor was found on the right. In November, axillary dissection on the left produced lymph nodes containing metastatic tumor. In February the patient noted back pain. This persisted, and it was thought that meningeal metastasis of tumor might be present.

The older child had a congenital absence of the hand.

The menstrual period had begun August 10. Hysterectomy was done on September 28. A rabbit test for chorionic gonadotrophin was positive on September, 26.

Embryonic Membranes and Embryo

The membranes and embryo were studied after fixation in formalin (figs. 4 and 5). The chorion, covered with villi, measured 34.5 X 33.2 mm. The yolk sac was a pyriform structure measuring 4.5 X 3.5 mm.. and was attached to the embryonic gut by an attenuated duct. The amnion was not measured; it was largely removed with the aid of jeweler’s forceps and iridectomy scissors. The body stalk was associated with the yolk duct in the region of the future umbilical cord.

By rotating the entire specimen shown in fig. 4 in a dish of formalin, the embryo was studied microscopically in all views except the dorsal. The embryo was 6.5 mm. in length (crownrump). The arm buds were elongated and medially flexed a bit. The leg buds were simple paddles. The glossopharyngeal swellings (bars) were hidden in part by the overhanging opercula (e.g., right and left hyoid bars). The otic vesicles had endolymphatic appendages. The developing optic lenses were invaginations which were continuous with the skin ectoderm and

fig. 4. Case 2. In this block of endometrium from the posterior uterine wall, the embryonic membranes and embryo have been exposed by a large window mode in the deciduo copsularis and chorion.

which communicated with the surface of the embryo via temporary “ostia.”

Comparison with Carnegie Embryos

The embryo was compared with two Carnegie embryos that one of us had studied, No. 836 and No. 3385 (Wells). Its morphologic development was more advanced than that of embryo 836 (4 mm., horizon XIII) and less advanced than that of embryo 3385 (8 mm., horizon XV). All of its observed features were like those of Carnegie embryo 814i (7 mm., horizon XIV, Streeter7). Accordingly, we regard our embryo as eligible for horizon XIV.

Estimated Age

The operation was done 49 days after the beginning of the last menstruation. The subtraction of 14 days gives a tentative ovulation age of 35 days, which is not in accord with the estimated ovulation age of the 34 embryos in Streeter’s horizon XIV, namely, 29 : 1 days (Streeter7). Therefore, following Streeter’s Pbservations, we estimated the ovulation age at 28 to 30 days.


Two superb human embryos, estimated to be 23 and 29 days old, are presented. They fall into Streeter’s horizons XI and XIV,


University of Minnesota Minneapolis 14, Minn.


l. AREY, L. B. Developmental Anatomy (ed. 6), Philadelphia, Saunders, 1954.

2. ATWELL, W. J. A human embryo with seventeen pairs of somites. Contrib. to EmbryoI., Carnegie Inst. Wash., 21:1, 1930.

3. HAMILTON, W. J., BOYD, J. D., and MOSSMAN, H. W. Human Embryology (ed. 2). Baltimore, Md., Williams & Wilkins, 1952.

4. HEUSER, C. H. A human embryo with 14 WELLS & KAISER

fig. 5. Case 2. Ventral aspect of the embryo. The drawing also shows lhe yolk sac and duct, the body stalk, and on unremoved portion of the amnion.

pairs of somites. Contrib. to Embryol., Carnegie 7. STREETER, G. L. Developmental horizons in

Inst. Wash., 22: 135, 1930. human embryos. Description of age group xiii, 5. PATTEN, B. M. Human Embryology (ed. 2). embryos about 4 or 5 millimeters long, and age New York, Blakiston, 1953. group xiv, period of indentation of the lens 6. STREETER, G. L. Developmental horizons in vesicle. Contrib. to Embryol., Carnegie Inst. human embryos. Description of age group xi, Wa.\'Iz., 31:27, 1945. 13 to 20 somites, and age group xii, 21 to 29 8. WELLS. L. 1. Development of the human diasomites. Contrib. to Embryol.. Carnegie Inst. phragm and pleural sacs. Contrib. to Embryol.. Wa.\'h., 30:21], 1942. Carnegie Inst. Was/1., 35: 107, 1954.