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The hand has a human-like palm, with the normal bones for that area. However, there is no thumb. In place of fingers, they have a set of unique structures. On both sides is a boneless digit like a thumb, which are capable of turning on where they meet the palm, and curving into a 90° arc. Between these digits is a single triangle of boneless flesh, about as long as the ring finger at the point. This structure is capable of folding down over the palm. The structure is at the end of a humanoid arm

hand

a rough diagram

How dexterous/useful could this structure be with modern tools designed for normal human hands?

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    $\begingroup$ I think that you could sketch a diagram to make the things clearer. $\endgroup$ Nov 28 '21 at 23:01
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    $\begingroup$ @ARogueAnt. Is the diagram clearer? Also, this question is not a duplicate; the other question specifies that the tentacles are long and able to grasp alone, unlike the digits of this hand $\endgroup$ Nov 28 '21 at 23:29
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It depends very much on the specifics of the tool.

  • On something like a smart-phone the structure might be just ad dexterous as a human hand for tweeting, swiping etc.
  • Might be reasonable to drive a car, as onl;y a moderate 'friction' grip is needed to handle a steering-wheel.
  • Would probably be OK for some mechanical tools - spanner, hammer, screw-driver. But likely could not provide as much force as an adult human hand. Other tools, like scissors might be just too poor a fit for practical use.
  • I doubt that it would be easy to hold or use a hand-gun or a trumpet.

In general, if you could handle the tool while wearing a mitten, then the limb would probably be OK - with caveat that the grip might still not be strong enough for some actions.

Note that an African elephant's trunk has

two distinct 'fingers' which they use to pick up and manipulate objects

The suggested limb end could easily be more dexterous than that. So while that doesn't answer the question of 'how could the limb handle tooles made for normal hands' (and you don't tend to see elephants running with scissors), it does illustrate that a 'fleshy' appendage can still be fairly strong and capable of fine and dexterous motor-control.

STOP PRESS ..,and in a very simple 'experiment' I have just confirmed that a human tongue (boneless fleshy appendage) can bench-press a weight in excess of 750g. Tongues are also pretty dexterous...

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While it is possible to create boneless structures that are dexterous enough, being boneless is going to create problem the amount of force they can exert for holding something, especially in a place as tight as the palm of one's hand.
Skeleton + muscles in general is a wonderful example of how tensegrity works - compression elements (bones) maintained in position by tension elements (muscles).

The human male anatomy offers an example on how well a relatively short muscle only organ performs mechanically - when rigid, it can't hold due to geometry, were it to be ... umm... dexterous, it couldn't hold by lack structure.

This is to say, the answer to "How dexterous/useful could this structure be with modern tools designed for normal human hands?" is "You can have higher dexterity, but you won't have as much force as a human hand, probably one or two order of magnitude lower" - e.g. can pick/hold the weight of an apple, cannot manipulate objects of 10kg or higher.


And before you object using the tentacles (or the elephant trunk) as an example - remember the form-factor? The tentacles are long enough to coil around the objects to be held.


As mechanical solutions to soft digits (take the principle of it and extrapolate from there to the "muscle, blood, somehow elastic tissues available, but no bones"):

pneumatic/hydraulic soft-grippers (here as an example).
enter image description here. Will require pressures over what the heart as the hydraulic pump is able to deliver (and this is where the comparison with the penes have relevancy) - so you will need a specialized organ t raise the pressure enough to make a hydraulic cavity under pressure act as a rigid element

You may have some chances if you replace those pneumatic/hydraulic actuators by "bulging masses of muscles" - but in this case you are going to seriously impede the dexterity, because the "muscle bulging" effect is way weaker (as exerted force) than what the muscle tension is able to generate. So that you'll need larger volumes of those bulging muscles, it will make that digit resemble the Michelin man.

(particulate) jamming grippers - (here as an example) - working on the same principle that makes a pack of ground coffee extremely rigid when vacuumed, yet losing integrity when opened. It may work as a substitute for a sort of reconfigurable bones. That is, if the muscles on the finger allow fine control (so fine muscle fascicles, interlaced over many directors and supported by a sophisticated nervous system) so that they can shape the mass of jamming particles (to become the bone) before applying the pressure to jam those particles in something rigid.
But even in this case you are limited by whatever the friction between those jamming particles can offer, which means:

  • either use vacuum and you'll be limited by what whatever the external pressure is (and the volume of particulates that you use) or use strong compressive muscles to pack them tight - which will seriously impact on the dexterity of the finger (very much like "muscle bulging" case).

  • the particles better not evolve into spheres or any other shape that don't jam properly - slim chance for that, the finger actions are supposed to be frequent and repetitive.
    Replacing the particles over time? Like how? Using blood flow for transport? Using other organs?
    "resharpening" them in place?

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    $\begingroup$ The comparison to a penis doesn't make much sense; penes aren't adapted for grasping, whereas these digits are $\endgroup$ Nov 28 '21 at 23:11
  • $\begingroup$ By what mechanism would your boneless digit can exist in an "adapted to grasping" state? There aren't many solutions to this problem and any of them will have impact on the holding force. $\endgroup$ Nov 28 '21 at 23:16
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    $\begingroup$ An elephant's trunk is boneless, but nevertheless is fairly dexterous and can exert considerable force $\endgroup$
    – Penguino
    Nov 28 '21 at 23:57
  • $\begingroup$ @Penguino should I specifically mention the form factor of the elephant's trunk in the same place I mention the tentacles or can you extrapolate from there? $\endgroup$ Nov 29 '21 at 0:01
  • $\begingroup$ I hav eadded an elephant trunk section to my answer. The point is not the entire trunk, but the bits at the end. $\endgroup$
    – Penguino
    Nov 29 '21 at 0:11

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