from the relative size of the liver becoming smaller.
Though the head appears large at first, and for a long time continues so,
yet its contents are tardy in their development, and until the sixth month
the parietes of the skull are in great measure membranous or
cartilaginous. Ossification commences in the base of the cranium, and the
bones under the scalp are those in which this process is last completed.
The contents of the scull are at first gelatinous, and no distinct traces
of the natural structure of the brain can be identified until the close of
the second month; even then it requires to have been sometimes previously
immersed in alcohol to harden its texture. There are many parts of it not
properly developed until the seventh month. In the medulla spinalis no
fibres can be distinguished until the fourth month. The thalami nervorum
opticorum, the corpora striata, and tubercula quadrigemina, are seen in
the second month; in the third, the lateral and longitudinal sinuses can
be traced, and contain blood. In the fifth we can distinguish the corpus
callosum; but the cerebral mass has yet acquired very little solidity, for
until the sixth month it is almost semi-fluid. (Campbell's _System of
Midwifery_.)
About the end of the third, during the fourth, and the beginning of the
fifth months, the mother begins to be sensible of the movements of the
foetus. These motions are felt sooner or later, according to the bulk of
the child, the size and shape of the pelvis, and the quantity of fluid
contained in the amnion, the waters being in larger proportionate quantity
the younger the foetus.
The secretion of bile, like that of the fat, seems to begin towards the
middle of pregnancy, and tinges the meconium, a mucous secretion of the
intestinal tube which had hitherto been colourless, of a yellow colour.
Shortly after this the hair begins to grow, and the nails are formed about
the sixth or seventh month. A very delicate membrane (membrana
pupillaris,) by which the pupil has been hitherto closed, now ruptures,
and the pupil becomes visible. The kidneys, which at first were composed
of numerous glandular lobules (seventeen or eighteen in number,) now
unite, and form a separate viscus on each side of the spine; sometimes
they unite into one large mass, an intermediate portion extending across
the spine, forming the horse-shoe kidney.
Lastly, the testes, which at first were placed on each of the lumbar
vertebræ, near the origin of the spermatic vessels, now descend along the
iliac vessels towards the inguinal rings, directed by a cellular cord,
which Hunter has called _Gubernaculum testis_: they then pass through the
openings carrying before them that portion of the peritoneum which is to
form their tunica vaginalis.
Public-domain text, read in full here on John Shaqi.
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