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FOETAL-MATERNAL
ATTACHMENTS
[Vol. XXV, Part II,
DISCUSSION
Amongst cotyledonary ruminants, the cotyledons vary remarkably in number,
size, form and structure according to the genus and species. The buffalo is a poly-
cotyledonary type, the number of cotyledons ranging from 42 to 147. The number
ranges from 160 to 180 in the goat and giraffe. In the oligocotyledonary type such
as the roe deer, the number is 5 or 6 [Amroso, 1952]. Sheep and cows occupy
an intermediate position, the number varying from 88 to 96 in the ewe [Ellen-
berger and Baum, 1921; Cloette, 1939] and from 70 to 142 in the cow
[Rorik, 1907; Sommer, 1912; Hammond, 1927]. Most authorities agree that
the cotyledons are arranged in rows in the gravid and non-gravid horns of the uterus.
In the buffalo they are arranged in linear arrangements (from six to two rows).
In the cow there is a similar arrangement (four rows in the body, three in the middle
of horn and two in the anterior extremity) [Craig, 1930] while in sheep the cotyle-
dons are arranged in four irregular rows [Grant, 1933].
The free surface of the ripe cotyledon (in the second half of pregnancy) also
varies with genus and species. It is markedly convex in the buffalo and cow whilst
it is concave in sheep and goat and less so in the blackbuck (Antelope cervicapara).
In the Baker's antelope, the cotyledons have flat surface and flat attachments
[Amroso, 1952]. The cotyledons of ruminants have been classified into those
exhibiting slender villi which branch at acute angles and those possessing broad villi
which branch at obtuse angles [Strah], 1912].
In the camel, the presence of the foetus in one uterine horn and a corpus luteum
of pregnancy in the ovary of the other horn is only a theoretical proof for migration
of fertilized ovum. In this respect, the original corpus luteum in the cow may atrophy
followed by the ripening and rupture of a second grafian follicle in the other ovary
accompanied by œstrus. This may be true also in the camel since quite a number of
visible follicles seem to be in a state of growth. In multiparous animals, such as the
sow, it is accepted as a final proof for ova migration when the number of foetuses
in one horn exceeds the number of corpora lutea in the corresponding ovary. In the
latter species there is a physiological tendency, when unequal ovulation occurs in
the two ovaries, to equalize the embryonic load in the two horns. Further research
in this field is needed.
There exists an evolutionary trend in the degree of intimacy between the foetal
and maternal blood. Eutherian mammals may be classified in five major classes.
In the camel, horse, donkey and hippopotamus, the chorionic epithelium comes in
direct contact with the maternal uterine epithelium. In ruminants (buffalo, cow,
sheep and goat), the uterine epithelium disappears leaving the chorion in contact
with the connective tissue of the endometrium. In the dog and cat, the uterine
mucosa is still further reduced and the chorion comes in contact with the endothelium
of the uterine capillaries. In the rabbit, rat and guinea pig, the membrane between
the two blood streams towards the end of pregnancy consists only of the endothelium
of the foetal capillaries. In primates the foetal blood is separated from the maternal
by three tissues of the chorionic villi.
The schematised diagrams are not accurate in every sense. Actually, all
placenta at the beginning of their development are of the epitheliochorial or primitive