[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: CRANIAL-CAUDAL vs ANTERO-POSTERIOR



Mike Taylor (mike@tecc.co.uk) wrote:

<I suppose the problem is not just with the change per se, but
that the new terms are such rubbish.  I mean really, different
terms for "the bit that faces forwards" depending on whether
you're talking about part of the skull or something somewhere
else.  Pah.  And _then_ naming the forward-within-the-skull
direction after a bone that only occurs in ceratopsians anyway! 
Honestly. You'd think that the term "rostral process" in a
theropod would refer to something that points in the direction
of the nearest Triceratops!  :-)>

  Evaluating use of terms for direction in elements in reference
to elements themselves:

  "rostral" refers to the snout, not the _os rostrum_.
Specifically, it is derived from the Latin _rostris_, mean nose
or muzzle (or snout, little difference), in any animal.

  As Darren Naish pointed out, animals with vertically-oriented
dorsal vertebral series confuse issues in regards to direction
when the same elements in a quadruped and a vertical biped are
not oriented the same way. Because of this, craniocentric
elements are exclusive to the cranium. Caudal is pertinent in
skulls, but rostral is preferable to anterior, and especially
when "cranial" or "towards the head" is irrelevant. Cranial and
caudal clarify when anatomical usage of "anterior" is towards
the chest in man, and "posterior" to the back or buttocks. Hence
the afforded usage of "posterior" when referring to one's butt.
When one's rostrum [read: nose] is directed in the same
orientation as one's venter, it is preferable not to use ventral
in referrence to the snout. Hence two systems in use,
conventional and the neo-orthodox.

  A case in point:

  One's teeth have two systems, depending on how you see them.
In a jaw, the most anterior tooth is the mesialmost. This means,
not that it is closest to the midline, but that it is closest to
the symphysis of the jaw. Mesial refers to the symphysis, not
the midline. Medial and lateral require use of a midline, but
then you get lingual/labial [or buccal, in mammals] in
referrence to the surface of the tooth facing the inside of the
jaw, or the outside. Hence, the mesialmost tooth in a jaw whose
symphysis is inflected at a right angle to the posterior of the
jaw (take Nigersaurus) and the carinae are then oriented
mediolaterally [side to side] or mesiodistally [toward/away from
the symphysis], but the use of a posterior and anterior carina
in posterior teeth become analogous to mesiodistal (or
mediolateral). The lingual/labial surfaces of the crowns remain
in those positions, because the tongue and lips have not changed
position, and the teeth remain between them. Even spinosaurid
conical teeth can be differentiated by their curvature as to
which is mesial and distal.

  Position and orientation change enough in small amounts to
require two, maybe three systems from which to refer to them
without confusion. If this becomes belated, and some simplified
form confuses the issue, present a description of a tooth's
function and relationship using only one system, then again
using the above terminology [describing the teeth of Nigersaurus
:)]. Which would become clearer? I have not tested this, so this
isn't a rhetorical statement.

----------

  I can distinguish an anterior caudal vertebra, by use of the
double noun "caudal vertebra," from a caudal anterior vertebra,
because the second phrase is ambiguous and tells you nothing
about the position. Previous examples are poorly defined,
because they use a double adverb to "elucidate" position, when
the posterior dorsal with a clear non-sacral-like morphology can
be termed "a posterior dorsal vertebra, anterior to the end of
the series." Perhaps someone can phrase this better. A
dorsosacral with more sacral-like morphology can be a posterior
dorsosacral. The term "dorsosacral" differentiates it from a
sacral _and_ a dorsal. Perhaps clarification on segmentation of
vertebral elements would work, as it does in snakes:

  atlantaxial cervical vertebra: primary vertebral elements,
articulating the column to the skull, intrinsic to skull
orientation and primary craniovertebral musculature;
  cervical vertebra: all cervicals post axial to cervicodorsal
elements, emphasized by the orientation of the prezygapophyses
and position of the parapophyses below the neurocentral contact
[Welles' definition];
  cervicodorsal [pectoral] vertebra: vertebrae bear a
parapophysis on the transition from centrum to neural arch;
  dorsal vertebra: vertebrae bear a separate parapophysis and
diapophysis, double rib facets;
  "lumbar" vertebra: single facet for the rib;
  dorsosacral vertebra: broaded transverse processes contact
ilium or with ribs that contact ilium, true ribbed dorsals which
are integrated into the sacral [synsacral] "subcolumn";
  sacral vertebra: the first up to three original sacrals which
possess broad transverse processes, no ribs, and generally
hypershortened centrum length, very deep neural canal for distal
ganglia; 
  sacrocaudal vertebra: caudals with distally expanded
transverse processes, no haemal arches, integrated into the
sacral [synsacral] "suncolumn";
  free caudal vertebra: caudals up to the transition point, with
haemal arches;
  pygal caudal vertebra: the distalmost caudals lacking
tranverse processes, or posterior to the transition point.

  If anyone has difficulty with these, please advise [onlist?
:)]

<Is it just me?>

  We get taught from preschool to integrate imperialistic
measure into our environment. We get taught on rulers that you
have to cut your paper so-and-so long, etc. We get taught on
liquid measure to buy a gallon of milk, not so-and-so pints.
Scientists get to learn all over, but yeah, we all Americans
(etc.) have an easier time to reading or feeling measure by feet
and ounces, not centimeters and grams.... You learn. I can read
centimeters automatically that I now have to calculate inches
over them, instead of the reverse. I can't get the feel for
kilograms or kilometers, but I couldn't measure a visual mile
anyway, or what a pound feels like.


=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

__________________________________________________
Do You Yahoo!?
Yahoo! Auctions - Buy the things you want at great prices.
http://auctions.yahoo.com/