From: eeb1@ellis.uchicago.edu (e elizabeth bartley)
Subject: Re: Another sentience que
Reply-To: eeb1@midway.uchicago.edu
Organization: University of Chicago Computing Organizations
Distribution: usa
Date: Thu, 20 Aug 1992 02:07:58 GMT

In article <1992Aug19.002422.19508@advtech.uswest.com>
stevens@eatdust (John Stevens) writes:
>In article <1992Aug15.172041.28780@midway.uchicago.edu>
>eeb1@midway.uchicago.edu writes:

>>My definition of "personhood" requires the ability for thought.  It's
>>a biological fact that zygotes and embryoes and early fetuses lack the
>>physical capacity for thought.

>Just to avoid a misunderstanding here, just what time frame are you
>refering to?  And how do you define thought?  I think you would be
>surprised at just how early the brain of a fetus begins to function. . .

>Certainly, many fetuses with active brains have been aborted.

Well, how do you define an "active" brain?  Firing neurons?  you can
get those in a test tube....

I don't see how one could have "thought" until the myelination of the
axons of the nerve cells in the brain had at least begun (the process
of myelination *continues* until adulthood); the nerve signal speed is
so much slower and there's so much more signal loss without the myelin
sheathing that I think the brain is basically not functional until
there's some myelination.

--- --- ---
_Clinical Embryology for Medical Students_, Third Edition
by Richard S. Snell, M.D., Ph.D., pp. 70-75

This is from a chart of the age of fetus and how developed various
systems are.  I'm including its "Gross appearance" and its
"Nervous system".

  Age     Gross appearance                       Nervous system
(weeks)
  1st     Fertilization
          Cleavage of zygote
          Blastocyst enters uterine
            cavity
          Trophoblast, inner cell mass
  2nd     Zona pellucida disappears.
          Blastocyst enlarges.
          Implantation.
          Syncytiotrophoblast and
            cytotrophoblast formed.
          Primary chorionic villi.
          Formation of embryonic disk,
            ectoderm, endoderm, amnion,
            and yolk sac.
          Extra-embryonic mesoderm.
          Extra-embryonic coelom.
          Primitive streak.
          Mesoderm and notochord.
  3rd     Head and tail folds                Neural plate.
                                             Neural folds.
                                             Partial fusion of neural folds.
  4th     Body narrow and tubular;           Neural tube.
            C-shaped.                        Three primary vesicles of brain.
          Connection with yolk sac very
            narrowed; limb buds appear.
          Placenta begins to form.
  5th     Head increases greatly in size.    Telencephalon.
          Face is forming.                   Diencephalon.
          Limb buds show limb, forelimb,     Mesencephalon.
            hand, or foot.                   Metencephalon.
                                             Myelencephalon.
                                             Cerebral hemisphere.
  6th     Head dominant.                     Flextures of brain obvious.
          Oral and nasal cavities confluent.
          Curvature of embryo diminished.
          Fingers and toes recognizable.
  8th     Head nearly as large as rest of    Rapid growth of central
            body.                              nervous system.
          Facial features more distinct.     Expansion of fore-brain vesicle.
          Eyes directed more anteriorly.
          Neck established.
          Limbs more developed.
          Digits of hands and feet
            separated.
          Fetus covered with epitrichium.
          Retrogression of tail.
  12th    Rapid growth in fetal length.     Brain and spinal cord well
          Head still relatively large.        developed.
          Eyes look anteriorly.             Cauda equina.
          External ears on side of head.    Filum terminale.
          Eyelids fused.
          Lanugo present.
          Nails.
          Sex recognition possible.
  16th    Further rapid growth in fetal     Cerebellum prominent.
            length.                         Myelination begins in spinal
          Eyes widely separated but           cord.
            eyelids fused.
          Auricles of ear high up on side
            of head.
          Fetus looks human.
  20th    Lanugo covers entire body.
          Vernix caseosa present.
          Hair present on head.
          Mother detects quickening.
  24th    Skin wrinkled and red.            Myelination begins in brain.
          Head still relatively large.
          Face child-like.
          Eyebrows and eyelashes present.
          Eyelids open.
  28th    Skin wrinkled.
          Subcutaneous fat appearing.
          Fetal contours more rounded.
          Hair on head longer.
  32th    Fetus looks wrinkled and scraggy.
          Lanugo hair has disappeared from face.
          Vernix caseosa thick.
          Nails reach end of fingers.
  36th    Fetus looks plumper and rounder.   Cerebral fissures and
                                               convolutions rapidly
                                               developing.
  40th    Fetus fully developed.             Lower end of spinal cord L3.
          More subcutaneous fat present.
          Lanugo hair disappear.
          Nails project beyond ends of fingers and toes.

--
Pro-Choice                 Anti-Roe                     - E. Elizabeth Bartley
            Abortions should be safe, legal, early, and rare.
Newsgroups: alt.abortion.inequity