Chapter 2. Prehension

36 WHAT IS PREHENSION?
Many postures in Table 2.1 demonstrate combined grips. One is
the closed fisted cvlindrical grasp with the thumb adducted
(Schlesinger, 1919). As a posture used to hold beer mugs (see Figure
2.6d), the thumb is placed on top of the handle, in opposition to the
radial side of the hand. This side opposition is combined with palm
opposition occurring between the fingers and the palm. This is similar
to the posture Napier called a power grasp (Figure 2.2a), where palm
opposition (between the palm as VF1 and the fingers as VF2) is combined
with side opposition (between the thumb as VF1 and the index
finger as VF2). In contrast, the coal hammer version of the power
grasp (Figure 2.2~) is not a combined grip, being purely palm opposition
between the palm (VF1) and the fingers and thumb (VF2).
Another combined grip is the dynamic tripod posture (Figure 2.4b),
which combines pad opposition between the thumb and index finger
with side opposition between the thumb and middle finger, while the
cleft acts as a VF3. Finally, the internal precision grip (Figure 2.4~) is
a combined grasp. Side opposition is used between the thumb and
middle finger, and palm opposition is used between the ring /little fingers
and the palm. The index finger, acting as an antenna, is a VF3.
Postures can be used as components of combined grasps. For example,
an adduction grip can be used in a combined grip. Patkin
(1981) described how a surgeon will at times stretch non-rigid tissue
between index and middle fingers (adduction grip) and thumb and
ringllittle fingers (see Figure 2.4). In this situation, the index and
middle fingers are holding the tissue in side opposition, while the
other fingers are using pad opposition to grasp the tissue. As noted
above, a finger-as-antenna or VF3 can be used in a combined grip.
For example, in the mug example (Figure 2.6), fingers pressing
against the outside of the handle (VF3) are an important component of
a grasp consisting of side or side/palm opposition.
Combined grasps are seen also in holding more than one object at
a time. For example, hooking a bag over the ulnar fingers as a VF3
leaves the radial fingers available for holding another object. Grasping
two chopsticks is another example. Kamakura et al.(1980) called this
posture a tripod grip - variation 2. This double grip holds one of the
chopsticks in a dynamic tripod (pad and side oppositions as noted
above) and the other chopstick in side opposition between the thumb
(VF1) and the palm, ring, and little fingers.
2.4 From Classification Towards Quantification
Taxonomies are a description, using nominal levels to classify