I'm afaid there is only speculation, for the most part, as to the
answer to this question!
You may read part of this article, describing how mammary glands may
have evolved from sweat glands. We do not have access to the rest of
??simple mammary gland includes those alveoli and ducts that empty
via one teat opening. Many mammals have multiple simple glands that
lead to separate openings in the nipple and empty independently.
So the external structure that we think of as a mammary gland of a cow
is a simple gland, that is her udder is made up of four ?quarters? or
four mammary glands. However, what appears to be a single gland of a
sow actually is a complex gland with two openings each leading to a
separate milk secreting simple gland.
?The best explanation is that the ancestors of cows gave birth to
more than one or two young and modern cows have retained extra
nipples. Actually the number of nipples in mammals varies from 2 to
19 (why an uneven number I do not know.) It is also a fact that 50% of
calves born to cows even have more that 4 teats. These are called
supernumery nipples and even occur sometimes occur in people.
Actually there is an advantage to having more nipples than young in
case one of them is infected or something.?
?Cows have four teats but goats and sheep only have two. All these
animals are badly designed because cows usually only have one baby and
mother cow has four teats whereas sheep often have three or even four
babies and the mothers only have two teats.?
?Cows do not necessarily have only four teats. In all mammalian
species, the mammary glands form on the ventral or underside of the
animal. The number of glands that an animal has is determined at a
very early stage of mammary development when the animal is a
developing embryo (see the resources section on Mammary Development).
In the developing embryo, the early developmental structures of the
glands form along a line on each side that is lateral to the ventral
midline, a little to each side of the navel. This means that the
number of glands that an animal will have is determined when it is an
early fetus. She will not grow more teats or glands during pregnancy
if she is carrying more than the normal number of offspring.
Where the glands and nipples form on an animal is determined by the
genetic programming of the species. For example, in humans and
elephants they form in the chest region, in guinea pigs and cows in
the inguinal (posterior) region, in mice in both the thoracic and
inguinal regions, and in pigs and dogs in the thoracic, abdominal and
?Question - Is it "teat" or is it "nipple"?
Both are referred to as Papilla mammae (a small nipple-like process of
the mammary gland).?
The above is taken from a very interesting module, that you may be
interested to read in its entirety:
?Teats vary in size, location, and structure in different mammalian
species. Female goats and ewes have two teats, each with a single
mammary gland, located between the hindlegs. Mares have two teats,
each with two mammary glands. The teats of the sow can be quite
variable in number, from six to thirty, and are located on two
parallel lines along the belly. Cows have four teats, each with one
mammary gland in the udder. Extra teats occur often, and are known as
supernumerary teats. They are nonfunctional and are usually removed
from domestic animals.?
More interesting reading:
Then again, since cows have four stomachs, maybe Mother Nature wanted
one teat for each stomach!
I hope this helps! If anything is unclear, please request an Answer
Clarification, and allow me to respond, before you rate.
evolution of cow udder
bovine udders + teats
why cows have four teats