nal epiblast. The foetus at term is surrounded by three membranes the deciduæ, reflexa and vera (derived from maternal structures); the other two, chorion and amnion, from foetal structures. The chorion is the median of the three membranes. Development. From the non-germinal epiblast, a single layer of cells springing from the outer layer of the blastodermic membrane.

Chorionic Villi.-The villi of the chorion are hollow at first, and are composed of an external epithelial and an internal mucoid layer. Later they contain blood vessels. Until the third month these projections into the maternal tissue abstract nutriment, oxygen, etc., from the deciduæ, and serve to keep the ovum in the upper portion of the uterus. After the third month hypertrophy of one portion takes place (chorion frondosum) to form the placenta; elsewhere the villi atrophy (chorion leve). The function of the chorion leve is to protect the integrity of the

ovum.

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ANOMALIES OF THE CHORION.

Placenta Membranacea.-The normal atrophy of a portion does not occur, and placental villi are developed over the entire surface of the chorion. Such placentæ are thinner than the normal.

DISEASES OF THE CHORION.

(a) Cystic Degeneration of the Villi.-This is an hypertrophy and myxomatous degeneration of the villi with the formation of cysts varying in size from that of a millet seed to a hen's egg. The old name of hydatidiform mole is not a good one, as mole is a meaningless term.

Frequency.-1 in 2000.

Mortality.-Over 13 per cent.

Causes.-Diseases of endometrium, or uterine wall; circulation of villi cut off by absence of allantois or its vessels. It may occur repeatedly in the same individual.

Symptoms.-Sudden increase in size of uterus at third or fourth month usually, hemorrhage, absence of foetus, and possibly discharge of cysts. It may be possible to feel the grapelike masses through the os uteri.

Causes of Death.-Hemorrhage, sepsis, perforation of uterus. Treatment. Is usually incompatible with foetal life. Hemorrhage controlled by tampon. If diagnosed early, abortion should be induced, as it assumes sometimes a malignant type and spreads to uterine wall, and thus has caused fatal hemorrhage and sepsis. This possible thinning of the uterine wall should contraindicate the use of the curette in unskilled hands. (b) Fibro-myxomatous Degeneration.-Up to the present time has been found only in the placental portion. (c) Chronic Inflammation.

The Umbilical Cord.

Development.-About the twentieth day after conception a diverticulum from the caudal portion of the intestinal canal is formed. It becomes constricted a short distance from its origin, the one portion to form the bladder; the other (larger) leaves the abdominal cavity with the omphalic or vitelline duct, and as an elongated cyst (allantois) rapidly grows and comes in contact with the entire chorion. Vessels soon develop, two arteries and two veins, which communicate with the villi of the chorion.

One of these veins disappears and the two arteries remain, These three vessels, with the omphalic duct, the remains of the umbilical vesicle, and the pedicle of the allantois receive a covering of mucous tissue (Wharton's jelly) and a layer of the amnion, and compose the umbilical cord. The fully developed cord at term is 20 to 21 inches in length, to inch in diameter, containing three tortuous vessels, one vein and two arteries, which possess valves.

The umbilical vesicle is the sac containing the nourishment of the embryo until the development of the chorion and placenta.

ABNORMALITIES OF THE CORD.

1. Length.-It may be very short (one centimetre), thus preventing descent of the fœtus or giving rise to hemorrhage from premature detachment of the placenta, or it may be very long (70 inches) and be found coiled around the foetus.

2. Thickness.-The cord may be almost as thick as one's wrist in places, from an excess of mucous tissue, the other constituent parts being normal.

3. Torsion.-Eight to ten twists normal. Due to twisting of arteries around veins. Usually has no effect. If extreme the blood vessels may be occluded. Great torsion usually occurs after the death of the foetus.

4. The Vessels.-There may be stenosis; atheroma; hypertrophy of valves; an overgrowth of connective tissue in the substance of the cord, as from syphilis; varicosities; rupture of the blood vessels, forming a hæmatoma as large, perhaps, as an apple.

5. Coils and Knots.-Loops and true knots may be formed, which are usually not tight. Intra-uterine amputation, not due to these, but to the formation of amniotic bands. The cord is found coiled around the neck about once in every four cases. Tangling of the cords in twin pregnancies and labors is not very uncommon. It is a dangerous accident to the children.

6. Insertion.-(a) Central is usual. It may be (b) marginal, or (c) velamentous (when the vessels run between the amnion and chorion before entering the placenta), or (d) meso-cord, when a fold of the amnion is arranged analogous to the mesorectum.

7. Hernia.-Due to arrest of development of lateral plates. 8. Cysts.-Due to liquefaction of the mucous tissue in the cord, or to apoplexies in the cord.

9. Calcareous Deposits. -In the blood vessels, or mucous tissue. Are often associated with syphilis, but of no significance.

10. Tumors. Some of the above-noted conditions are the cause of localized swellings: rarely a low-grade foetus amorphus may be attached to the cord so intimately as to look like a tumor in its substance.

The Deciduæ.

Development.-After the ovum is impregnated the mucous membrane of the uterus hypertrophies to tenfold its normal thickness, due to proliferation of young connective-tissue cells