Notes on Anatomy and Physiology: The Hand and The Tiger’s Mouth

Last time, we looked at how the bones of the elbow-forearm complex are designed so that the elbow bends and the hand turns.
To better understand the influence of the hand and elbow on the strength and balance of our entire structure, we need to consider the ties binding the components of the upper limb to one another and to the rest of the body.
As we proceed, we’ll see that the periphery, the outlying elements of the body, are powerfully entwined with the central and deep structures. The centre and the periphery are inseparable in fact, making the awareness of both vital to our art.
Today, we’ll look at the hand, its bones and arches, and some of its soft tissue layers.
The Bones of the Hand

Fig 1 A palm side view of the right hand. The bones are listed on the left, the joints on the right. It is the bones that we need to focus on for now. Neumann, page 245

The Hand’s Arches

The hand, like the foot, has three arches: the distal and proximal transverse arches running across the hand, and the longitudinal arch coursing along the hand’s length.

Fig 2 The two transverse and single longitudinal arches of the hand. Neumann, page 249

The distal transverse arch lies where the fingers meet the metacarpal bones of the palm. The flexibility of this arch allows the palm to flatten as the hands open and go out in the tor yu with the fingertips up. And with Whip To One Side, it permits the outside first, fourth and fifth metacarpals of the right hand to fold about the more fixed second and third metacarpals while the tips of the fingers come together to form a beak. The two central metacarpals form the keystone of the arch.

The proximal transverse arch arises from the bones of the wrist. Although much more rigid than the distal arch, it opens and flattens over time as a result of placing the hand in Tiger’s Mouth. Gradually, the appearance of the heel of the hand changes.

The longitudinal arch, running the length of the hand, is centered about the second and third metacarpals which run to the index and middle fingers. Stiff at its proximal end where it joins the wrist, this arch is very mobile distally, as active flexion and extension of the fingers demonstrate. Each arch supports the other two, illustrating how elements weave together for strength.

The Soft Tissues of the Hand

Thus far, we’ve referred to the bony architecture of the hand. But layer upon layer of soft tissue contribute to the hand’s structure as well – sheets of fascia, tendons, tendon sheaths, muscles, nerves, arteries, veins and lymphatics.

Without worrying about the names of all these constituents, let’s look quickly at four drawings from Netter that give us a sense of those layers. These are views of the front of the hand; similar layers also exist at the dorsal aspect of the hand.

Don’t get lost in the details. Just note that these successive layers exist beneath the skin of your palm. And because we may not describe this for other regions of the body, remember that this complexity is found everywhere. Which is why we keep things simple and work with metaphors like Tiger’s Mouth when we play at tai chi.

Fig 3 Peeling back the skin, we encounter a sheet of dense connective tissue, the palmar aponeurosis. Most of the muscles of the hand lie deep to that fascia. Netter, plate 459

Fig 4 Once the palmar aponeurosis is removed, we find muscles as well as the sheaths that surround the tendons of the extrinsic muscles lying on this side of the hand. The extrinsic muscles originate from the forearm or the humerus and flow down into the hand. Netter, plate 460

Fig 5 Deeper still, we find the intrinsic muscles of the front of the hand. These are the small muscles that begin and end their journey in the hand itself. Netter, plate 465

Fig 6 The arteries and nerves of the palm. Netter, plate 466

Having spent a few moments reading about anatomy, move one of your hands from a position of rest into Tiger’s Mouth. Feel each of the three arches open up and note the increased sense of structure. Imagine how the Tiger’s Mouth engages all the soft tissues of the palm depicted in the drawings above, elongating them and creating an elastic or return force in the process.

Notice, too, how stretching out all these tissues creates a flow of sensory information into our central nervous system. The hand is an extremely important sensory organ, so important that a large part of the sensory cortex of the brain is dedicated to it. Work done by Dr. Penfield, a Montreal neurosurgeon, gave us images known as sensory and motor homunculi.

A homunculus is a representation of the whole human form, based in this case on the area of cortex devoted to sensing or moving the various body parts.

Fig 7 On the left, the sensory cortex of the right cerebral hemisphere; on the right, the motor cortex. Notice the large area reserved for the hand in each instance.

In a very real sense, then, the body has another existence in the brain. The hand, for example, is as much a network of sensory nerves in the brain as it is a physical form.

Another way of expressing the value attributed to sensation coming from the hands is to create an image of what the body would look like if each part grew according to the area of the brain concerned with its sensory perception.

Fig 8 A sensory homunculus of the human body based on the amount of brain dedicated to the sensory perception of each of its parts.

So the hand is a major sensory organ, one that is equally capable of a vast array of intricate movements. When we use our hands with intention in the set, we become more aware of where our hands are and of what they are doing. This enlarges the area of cortex devoted to the sensory data streaming in from the hand. This, in turn, leads us to become even more mindful of the hands. Neuroplasticity in action.

And because the hands are connected to the rest of the body, much like the tip of a whip is linked with its handle, we can use them not only to sense the outer edges of our upper limbs but to increase awareness of the spine, pelvis and feet.

1. Kinesiology of the Musculoskeletal System, Foundations for Rehabilitation, Second Edition, 2010, Donald A. Neumann, Mosby Elsevier, ISBN 978-0-323-03989-5

2. Atlas of Human Anatomy, 4th Edition, Frank H. Netter, 2006, Saunders Elsevier, ISBN 13: 978-1-4160-3385-1

Bruce McFarlane MD

© Taoist Tai Chi Society of Canada


Filed under Anatomy and Physiology, Health Watch

9 responses to “Notes on Anatomy and Physiology: The Hand and The Tiger’s Mouth

  1. Opening the hand in the Tiger’s Mouth position has an effect on the acupoint located in the web of soft tissues between the thumb and index finger. This point (named “Hegu or “Joining Valley”) is considered to be one of the primary points for invigorating the smooth flow of Qi and Blood throughout the body, and to “release the Exterior”, or, in other words, to promote sweating in order to expel invading pathogenic factors such as Wind, Cold or Damp which may obstruct the usual passage of Qi, leading to painful syndromes.

    Hegu is not alone. Located between each of the other fingers is a similar point, which when added together form a collection known as the Eight Pathogens, or Baxie (ba-shier), there being four on each hand. Spreading the fingers along with the Tiger’s Mouth helps to activate all eight points. This is useful as the meridians change direction at the fingers, so spreading all of the fingers helps to make sure that the Qi passage is unobstructed.

    The opening and flattening of the hand as mentioned in the main text, stimulates a point between the metacarpals of the index and middle fingers, found on the palmar surface when the tip of the middle finger touches the palm on making a loose fist. This point, Laogong, mirrors the “Bubbling Spring” point on the sole of the foot, and is thought to be an eminent point for calming the mind, especially when sadness or anger predominates.

    • Ellen Rice

      I read the articles about the hand and the forearms yesterday and I do not claim to understand all the details – I glossed over them as instructed. I very much enjoyed the homunculus diagrams as they are funny and informative. I did not understand at all what you were talking about in the rotation of the lower arm positions in the tor yu until I went to class and my instructor demonstrated what we were to work on and then the penny dropped. It is so satisfying when things happen and they are right! I appreciate learning about the anatomy in the practice of tai chi. As a fairly recent student of the art, I think it enhances my personal experience of tai chi by enabling me to fine tune my movements better. I will continue to learn about the anatomy as I am able and as long as you provide the information. Thanks. I am very interested in the calming of the mind effect of the middle finger to the palm in David Kemp’s response above. Counter intuitively, my blood pressure has gone sky high on some occasions and I have felt overstimulated at the end of some tai chi sessions. I started tai chi for expected calming effects which haven’t always happened but my improved ability to balance and and do because of my increased physical strength through practice have kept me coming to classes even though I’ve been somewhat confused by the stimulating rather than calming effects of the play.

  2. Dave Latham

    I look forward to each installment of Dr. Bruce. Although not being of a medical background myself, I get to think more about the effects of tai chi on the body. I am very please to see the additional comments of David Kemp sharing the eastern medical background of the cause and effect of thai chi exercise. This is an added bonus that I would hope will continue in the future installments of the Tigers Mouth.
    Keep up the good work and thank you.

  3. Ellen Rice

    Thank you for your response and the clarification David Kemp. The Yin Yang explanation for the overstimulation I feel makes sense to me as it is after the nighttime classes that I feel overstimulated as well. I do not want to stop attending classes but the difficulty settling is is unsettling. I went to a workshop yesterday and was informed that Master Moi spoke of a sleeping meditation so that Tai Chi could be done 24 hours a day and not just during waking hours. I wonder who teaches that meditation? Something worth exploring.

  4. Pat

    Mr homunculus clearly conveys the considerable value of working with the hands!

  5. Now I know why I have experienced and felt having hands as if they were ballooned out the size of baseball mitts during extensive tai chi.
    The homunculus is worth a thousand words.

  6. M.Gottlieb O. Mittelstädt

    Dear Dr.McFarlane,

    I enjoyed the your article on the hand and the tiger’s mouth as well as the comments of my fellow Taoist Tai Chiists regarding that topic.It explains also why Master Moy holds his hands as he does in the video clip that shows him,on this site,doing a 15 minute demonstration of the complete set.

    I am a member of the Taoist Tai Chi Society’s Burlington Branch and saw the folder with your articles in our chapter’s exercise location.I searched in the folder for a similar coverage of the knees and feet,especially with regards to their reactions and their internal happenings during tor yus and don yus and other moves in the set requiring rotation.I am concerned about their effects.My questions that I directed to the instructor were answered but an article like the one you wrote on the Tiger’s Mouth would be more thorough and enable its reader to follow up on remaining questions.

    Could you please let me know where I can find information on the above topics.

    I thank you and remain,

    sincerely yours,

    Martin G.O.Mittelstädt.

  7. Thank you for the information. Been practicing Tai-Chi for a couple of months now, and experiencing the benefits of regular practice. I am finding out I have to continually empty my cup as I come from a different background practice… Really enjoying Master Moy’s teachings and skill…

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