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Re: How did dromaeosaurs use their arms?



I wrote:

<<Ostrom (1976) showed the arm supination/pronation
was limited, due largely to the wrist, whereas in less
derived theropods, such as allosaurs, it was more
capable of s/p. Such ways, the wrist was constantly
held in line with the proximal ends of the
ulnae/radii. Such a structure would allow the wrist to
fold easily against the forearm, pulling it out of the
way, and allowing sufficient leverage for a powerful
forward "swap" of the hand, to be simplistic.>>

Henri Rönkkö wrote:
 
<Supination/pronation means folding the wrist upwards
and downwards, not sideways, right?>

  Supination is the result of turning the distal ends
of the ulnae or radii away from the neutral "prone"
position your hand would be in if you just stuck yur
arm up, without muscles acting on the bones. Pronation
is the reverse, with the muscles acting in such a way
as to bring the distal and proximal ends in alignment.
Laying on your back is the prone position, while
twisting your upper torso in this state is the supine
position; similar for the arm, leg, etc. As far as I
can tell, only sciurids can completely supinate their
lower legs, turning the foot backwards when climbing
down a tree trunk.

<<is turned dorsomedially, and the first phalanx was
"twisted" slightly along the axis with the distal
articular turned medially, so that the digit would>>

<I didn't quite understood this. I know that "dorsal"
means the upper half of an animal, "medially" probably
something like "in the middle" and "in axis with
something" in turn that a thing has the same direction
as something else.>

  Dorsal means above the vertebral axis, or towards
the neural spines, and away from the neural canal;
towards the top, with the vertebral column acting as
the relative structure; away from the ventral. In the
hand, the back of it is the dorsal, the palm the
ventral, etc., but orientation problems give us the
terms flexor (towards the curving of the fingers) and
extensor is the opposite, also palmar for the palm,
and so on. Medial means towards the midline, and can
occur in a single bone, or the whole animal. An
unpaired bone, such as our fused frontals, would have
medial along the middle of the bone, as you suggest,
in the middle.

<<have faced partially inward with the arm extended,
or down when flexed. The other two digits would have
faced down in the former, and inward inward in the
latter, though the third finger may have been much
more mobile.>>

<What do we mean here with "inward" and "down"? I
think that if I hold my manus horizontally, so that
the inside of it faces down, the fingers II-V of mine
face BOTH down AND inward.>

  Depends on _how_ you hold it, or what you're using
as a point of reference. If your own body, the hand is
perpendicular to your long axis, but parallel to the
ground, and the term "inward" does not apply; if the
ground, then it's "down."

<The thumb of mine, in turn, faces as wuch inward as
it faces downfard. I am not trying to point out any
kind of functional analogies here, just making sure
that we mean the same things with same words.>

  Techinically, your hand faces "down," but
perpendicular your your vertebral axis, which will be
assumed to be vertical and perpendicular to the
ground, thus your hand, if horizontal, will be
parallel to the ground, and faces only "down." The
fingers 2-5 will similarly face downward, barring a
unique condition; the thumb neutrally faces laterally
(away from the midline, in the same direction as and
arrow oriented towards the outside of your body at
right angles to the dorsal and vertical arrows
(sagittal plane)) and towards the ground, and in a
quadruped, would be termed "lateroventral", but in us
would be laterally and "down."

  In maniraptorans, the pollex (thumb) is the
opposite, and faces "down" and in line with the second
digit (index) in neutral extension, but during
flextion, the ginglymoid articular surface of the
first metacarpal to which it articulates forces the
phalanges to rotate laterally as the muscles pull it,
and the claw (for relativity) is oriented medially.

  Now, the terms would change given the manus'
position to the body and the ground, as happens given
the condition of the wrist and forearm bones -- the
manus is held in a vertical position, pointed backward
(caudally), and in this way, the fingers all more or
less would face flexorly medially, the fist finger
slightly towards the ground, and thus medioventral to
the long axis of the maniraptoran.

  During extension of the arm, the forelimb
experiences little axial twist (supination), but the
humerus may allow the limb to orient upwards, rather
than in line with the sagittal plane; if the arm were
held outward, the palm, second and third fingers would
face ventrally, towards the ground, and the first
digit would face slightly laterally; extension of the
arm while elevated (in this position) would reorient
the first digit in front of the hand, or anteriorly,
cranially.

  Without elevation of the arm, the forelimb in
extension would make the palm, second and third digits
face medially, but the pollex would face either
anteriorly, or in extreme extension, up or dorsally.

  I hope this clears up the terminology issue,

=====
Jaime "James" A. Headden

"Come the path that leads us to our fortune."

Qilong---is temporarily out of service.
Check back soon.

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