Paper - Placenta praevia in a rhesus monkey (1939)

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Palmer A. Placenta praevia in a rhesus monkey. (1939) J Anat. 73: 626-629. PMID 17104785

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This historic 1939 paper by Palmer describes the placental abnormality of placenta previa in a rhesus monkey.

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Placenta Praevia in a Rhesus Monkey

By A. Palmer,

Rockefeller Research Fellow From the Department of Human Anatomy, Oxford

Piacenta praevia occurs in about 0-1%, and the central type no more frequently than in 0-02 % of human births (Williams, 1936). To my knowledge no variety of the condition has ever been reported in subhuman Primates, and for that reason an account of central placenta praevia in a rhesus monkey (Muataca mulatta) is presented in the following paper.

The normal placenta in the rhesus monkey consists of two disks. The larger disk constitutes the primary placenta and the umbilical cord is invariably attached to it. The secondary and smaller disk, which only rarely is completely absent, is supplied with blood through vessels that pass along the membranous chorion separating it from the primary placenta (Wislocki, 1929).

Case History

A female rhesus monkey (DB 1081/28) that had been in the Gardens of the Zoological Society of London 2 years and 8 months, died from secondary anaemia following a profuse vaginal haemorrhage on the night of 80 November 1928. Keepers reported that she had been perfectly well during the day of 80 November. There were blood clots in the vagina and marked pallor of all mucous membranes. The animal appeared to have been in the first stage of labour and to have died of haemorrhage from a placenta praevia. The fact that the animal was pregnant had not been recognized, nor was there any history of a previous pregnancy. The post-mortem examination (which was made by Dr S. Zuckerman) revealed no evidence of acute infection. All organs were pale and “washed out’. Pathological findings were otherwise restricted entirely to the uterus and its contents. An apparently full-term uterus, free, except for its normal pelvic attachments, was found filling the abdomen.

Description of the Specimen

(after fixation in formalin and preservation in alcohol for 10 years)

The specimen consists of the entire uterus and the fleshy birth canal. The outer surface of the uterus is uniformly smooth except for a somewhat increased vascularity along the left side of the lower uterine segment. The specimen was opened by an anterior longitudinal incision. The cervix is patulous with the placenta presenting. A full-term female foetus is present in the LOA position. It has a sitting height of 145 mm. and weighs 247 g. The umbilical cord measures 16 cm. in length. Other measurements are as follows: greatest uterine width, 10-2 cm.; thickness of uterine wall in the fundus 3 mm.; distance between top of fundus and internal cervical os; length of cervical canal 2 cm.; and length of vagina approximately 5-5 cm.

The placenta has the form usual to rhesus monkeys, and the umbilical cord is inserted slightly eccentrically into the larger of the two disks. The superior margin of this disk is attached 4 cm. above the internal os along the left lateroposterior surface of the uterus, and nearly half of it has herniated into the cervical canal, having been torn from what had apparently been its firm attachment to a closed internal os. At the internal os on the right side its inferior margin joins the smaller disk, which is attached to the right side of the lower half of the uterine wall above the internal os. The inferior margin of the smaller disk is also partially separated and it lies in the upper part of the cervical canal. Non-vascular membrane and superficial vessels are the only communicating structures between the two disks.

Text-fig. 1. Central placenta praevia in rhesus monkey.

The larger disk measures 6 x 11 cm., and the smaller one 5 x 9 cm. The part of the larger disk lying in the cervical canal measures 4x 5 cm. The average thickness of the placenta is slightly less than 1 cm., and in all it weighs 75 g.

Microscopic Examination

All tissues are slightly infiltrated with white blood cells. The lower part of the cervical canal is otherwise normal in appearance, and the line of transition between the vaginal epithelium and the cylindrical cervical epithelium occurs in the middle third of the canal. The cervical stroma contains a few cervical glands which are distended with mucus. The mucosa of the upper third of the canal, although it is unrelated to the site of placental implantation, is deeply plicated (Pl. I, fig. 1), and its superficial stroma is more cellular than usual (PI. I, fig. 2). The cells are polygonal and have fairly distinct cell walls, and this fact, coupled with their network arrangement, suggests that this region of cervical stroma has undergone a modified decidual reaction. It may be noted that swollen decidual cells have been described in the human cervix in cases of placenta praevia (Morton, 19387).

Several large and thick-walled vessels are to be seen in the myometrium of the placental site (Pl. I, fig. 3). Their walls consist almost entirely of many layers of swollen epitheloid cells which appear to have undergone a decidual change (PI. I, fig. 4). The large amount of cytoplasm in these cells appears to distinguish them from the supposed endothelial proliferations which occur in early pregnancy in the uterine vessels of the macaque (Fig. 47 in Wislocki & Streeter, 1988). The preparation of the material appears to have caused dissolution of cytoplasmic granules and a shrinkage of cells within a fibrous matrix. It is probable that this vascular reaction is equivalent to the alterations which occur in the vessels of the human uterus in preparation for their postpartum closure.

It may be noted that cells similar to those described in the preceding paragraph occur in the walls of arteriovenous anastomoses (Schumacher, 1988). It is generally believed that these cells are differentiated within the media, and that in spite of their epithelial appearance, they are not derived from the endothelium as Wislocki &.Streeter suggest they are in the vessels of the pregnant uterus. This view depends upon the fact that, in arteriovenous anastomoses a distinct and continuous layer of differentiated epithelioid cells covers the large cells to which a chemical or hormonic function, in addition to a mechanical one, has been ascribed.


A case of central placenta praevia in a rhesus monkey is described. Among the points of interest noted are a modified decidual reaction in the cervical stroma and the presence of thick-walled vessels in the myometrium of the site of placental implantation.

My best thanks are due to Prof. W. E. Le Gros Clark for his generosity in furnishing facilities for working in his department, and to Dr S. Zuckerman for permission to describe the specimen.


Morton, D. G. (1937). "Anatomic description of marginal placenta praevia with a discussion of etiologic implications." Amer. J. Obstet. Gynaec. vol. Xxx, p. 547.

Scuumacuer, S. (1938). ‘‘Uber die Bedeutung der arteriovenésen Anastomosen und der epitheloiden Muskelzellen (Quellzellen).”’ Z. mikr.-anat. Forsch. Bd. xu, S. 107.

Wiut1ams, J. W. (1936). Obstetrics (revised by H. J. Stander), 7th ed. New York and London: D. Appleton-Century Company, Inc.

Wisocxl, G. B. (1929). ‘‘On the placentation of Primates, with a consideration of the phylogeny of the placenta.’’ Contr. Embryol. Carneg. Instn, vol. xx, p. 51.

Wistockl, G. B. & STREETER, G. L. (1938). ‘‘On the placentation of the macaque (Macaca mulatta) from the time of implantation until the formation of the definitive placenta.”’ Contr. Embryol. Carneg. Instn, vol. XXVU, p. 1. Journal of Anatomy, Vol. LX XIII, Part 4 Plate I Fig. 3.

Plate 1


Fig. 1. Photomicrograph showing plication of cervical mucosa in upper third of cervical canal. x 60.

Fig. 2. Photomicrograph showing modified decidual reaction in superficial stroma of cervix; enlarged from Fig. 1. x 450.

Fig. 3. Photomicrograph showing occluded thick-walled maternal vessel in the myometrium of the

placental site. 75. Fig. 4. Photomicrograph showing decidual-like cells in wall of vessel. x 450.

Cite this page: Hill, M.A. (2024, April 17) Embryology Paper - Placenta praevia in a rhesus monkey (1939). Retrieved from

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