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DEVELOPMENT OF THE FOETUS AT DIFFERENT PERIODS OF GESTATION 341
processes. Being very small and minute, it can hardly be detected hi abcrtions when
surrounded by blood clots.
Second Month (Eighth Week).—At the end of *he second month the ovum is If
inches long about the size of a hen's egg, and weighs two to five drachms. The embryo
measures £" in length. The mouth and nose are separated, the umbilical vesicle has
disappeared and the generative organs are apparent, but the sex is indistinct. The anus
appears as a dark spot. The cord is longer and the placenta has commenced to form.
The centres of ossification have begun ha the mandible (lower jaw), clavicle, ribs and
bodies of the vertebrae.
Third Month (Twelfth Week).—At the end of the third month the fcetus is 3 to 4
inches long, and weighs about one ounce. The placenta is developed and chorionic
villi have atrophied. The cord is much longer, and has a spiral twist. The head is more
rounded and separated from the body by the formation of the neck. The eyes and the
mouth are closed. The nails ha the form of thin membranes appear on the fingers and
toes. The sex is still indistinguishable. The heart is divided into two chambers, and
the alimentary canal is situated within the abdominal cavity.
Fourth Month (Sixteenth Week).—Towards the end of the fourth month the fcetus
is 4 to 6 inches in length, and is 2 to 4 ounces in weight. The sex can be differentiated.
The skin is rosy and firmer. Down begins to be formed on the body. The head is one-
fourth of the length, of the body. The convolutions of the brain are commencing to
develop. The membrana pupillaris is visible. The skull bones are partly ossified, but
the sutures and fontanelles are very wide apart. The gall-bladder is forming, and
meconium is found in the duodenum. The umbilicus is situated near the pubes. The
centres of ossification are present in the lower segments of the sacrum, and the ossicles
of the ears have ossified. ^
Fifth Month (Twentieth Week).—The fcetus of the fifth mon^i is 7 to 10 inches long,
and weighs about eight ounces. Light hah" is seen covering the head which is about
l/3rd of the length of the fcetus. Lanugo is quite distinct on the body. The nails are
distinctly marked, but are very soft. The germs of the permanent teeth begin to appear
in the jaw. The position of the umbilicus recedes upward. The centres of ossification
are present in the os pubis, os calcis, and ischium. Yellowish, bile-stained fluid is found"***
in the small intestine, and meconium of a yellowish-green colour at the commencement
of the large intestine.
Sixth Month (Twenty-fourth Week).—Towards the end of the sixth month the
fcetus is 9 to 12 inches long, and weighs 16 to 24 ounces. The body is cinnabar red in
colour, and the skin has a wrinkled appearance for want of fat in the body, though a
small degree of fat is beginning to deposit in the subcutaneous cellular tissue. Cerebral
hemispheres cover the cerebellum. The eyelids are adherent and the membrana pupil-
laris still exists. The eyebrows and eyelashes are beginning to form; the umbilicus
is situated farther from the symphysis pubis. The testicles are lying close to the kidneys.
Dark meconium is found in the upper part of the large intestine. The centres of ossi-
fication are present in the four divisions of the sternum.
Seventh Month (Twenty-eighth Week).—The fcetus is 13" to 15" long, and wei^is
2 to 4 pounds. The skin is dusky red, thick and fibrous, and covered with vernix
caseosa, which is a white fatty substance formed of epidermal scales, lanugo and the
secretion of the sebacious glands. The eyelids are open, and the membrana pupillaris
has almost disappeared. The nails are thicker, but do not reach the ends of the fingers.
Meconium occupies nearly all the large intestine. The testicles are in the act of descent,
and are found in the external inguinal ring. The centre of ossification is in the
Eighth Month (Thirty-second Week).—At the end of the eighth month the length
of the fcetus is about 15 to 17 inches, and the weight from 3 to 5 pounds. The skin is
rosy, covered with soft hair, and is not wrinkled in appearance, as there is more sub-
cutaneous fat under it. The hair of the scalp is denser, and the lanugo has almost
disappeared from the face. The membrana pupillaris is no more visible; the nails have
reached the ends of the fingers. The left testicle has already descended into the scrotum,
but not the right. The centre of ossification is found ha the last vertebra of the sacrum.
This is the most important month from the medico-legal point of view as the child
becomes viable at the end of the thirtieth week, ie. at the 210th day,
Ninth Month (Thirty-sixth Week).—At the end of the ninth month the foetus is
about 18 inches long, and weighs 5 to 6 pounds. There is no more senile appearance of
the face. The scalp is covered with hair, while the down on the body has disap
The scrotum contains the testicles, and is wrinkled. The vulva is closed. Vernix
is found in the flexures of the joints. Meconium is found at the termination of fte
intestine. The centre of ossification commences to form in the lower epipltyssls
femur from the commencement of the ninth month.
Tenth Month (Fortieth Week).—The fcetus presents the signs of
term) child. The length is from 19" to 20", and the weight fram 6 &*