To me – to you: directions and descriptions

Having covered the ongoing saga (though to be honest it’s less of a saga than a small novella) of the ‘cranial-caudal’ descriptions issue, it seemed an appropriate time to bring up the ideas of directions in anatomical descriptions. As I noted in the earlier post, the point about directions in anatomy are to be clear and concise and to provide an unambiguous definition of something to avoid confusion for the readers and researchers who want to follow what you have written accurately.

It should be easy to see how people can get confused without being careful about terms. You could describe a feature on a humerus say as being on the same side as the thumb, but rotate your wrist and suddenly that point of reference disappears. Most people would describe their chest as facing forwards, but in a quadruped that same structure (the ribcage) would be facing down towards the ground, and while the metatrsals in our feet face flat down on the ground in most other animals they would face backwards. If you used terms like this it would be easy to get lost or end up comparing the wrong things hence the general standardisation of terms. I say general of course as there are still issues here and there that crop up, like the cranial-caudal one, or those of the scapula.

So here as a brief guide / aid memoire, are a few of the basic directions used in anatomical descriptions for the orientation and position of bones and their features. Please excuse the very basic outline drawing, it was the best I could do* quickly:

Anterior (or cranial) – towards the head end of the animal.
Posterior (or caudal) – towards the tail end of the animal.

Dorsal – towards the back.
Ventral – towards the front.

Medial – towards the midline (something can also lie medially like vertebrae).
Lateral – away from the midline.

Proximal – towards the body.
Distal – away from the body and towards an extremity (so you can also talk about the distal tail for example).

Palmar (or plantar)> – towards the palm of the hand / sole of the foot.
Dorsal – towards the back of the hand / top of the foot.

Labial – towards the lips or outer part of the mouth.
Lingual – towards the tongue or inner part of the mouth.

These rather obviously all come in pairs of opposites but they can be used together or in combinations. So your spine is medially positioned and runs anterio-posteriorly (from front to back) and while your orbits face anteriorly (or rostrally if you prefer) you can swivel your eyes to face dorso-laterally (up and to the side) or medio-ventrally (down towards the middle) if you so choose.

The point is, and should be, that even as joints move and rotate and even whole body plans change and evolve (humans stand rather differently to monkeys, let alone cats or mice) the points remain relevant and accurate and directly comparable. Thus providing a secure set of references to make both descriptions and comparisons accurate.

*and by ‘do’ I mean ‘bother with’, but for this it should be more than sufficient.

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4 Responses to “To me – to you: directions and descriptions”

  1. 1 qilong 25/11/2009 at 7:44 am

    Oh, Dave, you should include that in your illustration of the dentition, teeth at any position of the jaw can have a different direction that is nonetheless labial, but moreover that teeth are also oriented with mesial and distal qualifiers, relative to their position and their orientation.

    Personally, the “cranial/caudal” dichotomy seems the most dynamically charged, as the proximal/distal and anterior/posterior dichotomies are caught up in it depending on the element, association of elements, relation of an element to a system (including a skeleton), and there being little attempt to discern these arguments from one another by any given author (with a rare exception or two). Annoying, so annoying.

    • 2 David Hone 25/11/2009 at 8:43 am

      Well I was trying to stick to the very basics. I have a whole post in prep on tooth characteristics and I’ll try to cover all that and more at some point, but yes, well worth noting here.

  2. 3 Mike Taylor 27/11/2009 at 12:46 am

    My favourite complex of confusing anatomical directions (as described in Taylor 2009:787): many different sets of directions have been used to describe sauropod coracoids, with the edge furthest from the scapular articulation having been variously described as median (e.g., Seeley, 1882), inferior (Riggs, 1904), anteromedial (Powell, 1992), distal (Curry Rogers, 2001) and anterior (Upchurch et al., 2004), and the designation of the other directions varying similarly.


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