Abstract
Microdissection studies were done on 30 human adult hands and serial sectional investigation and neuromuscular spindle counts done on 132 intrinsic hand muscles. Neuromuscular spindle distribution charts were drawn for all the intrinsic muscles except the adductor pollicis; a corres-ponding extrafusal fibre relative length chart is also presented. A discussion of the methodology employed for spindle count and distribution charting is presented. The limitations of the spindle density values obtained by different methods is also discussed and an alternative numerical index or ratio is suggested. From the results several following conclusions have been drawn and emphasised: (a) There is a close correlation between zones of high neuromuscular spindle concentrations and the longer extra-fusal fibres within each individual muscle, and this association appears to be of functional significance. (b) There appear to be special qualitative features, within the biomechanical arrangement of the muscles of the thumb, index and middle fingers (the "precision tripod",) not seen on the ulnar side of the hand. (c) The lumbrical muscles have uniquely higher neuromuscular spindle densities than the other intrinsic muscles. The lumbrical attachments, bridging the flexors and extensors of the hand, and the simultaneous mobility of their origins and insertions on the tendons of these other muscles in theory renders them additionally sensitive to finger movements. Their motor role, on the other hand, appears of somewhat secondary and incidental nature, although so far attention seems to have been focussed upon the latter more than on the sensory role. Other results have been presented which indicate that there may be variations in the functional predominance of the wing or phalangeal tendons over the other. A scheme of the operative forces has been proposed with respect to this. Finally two convenient sites for muscle biopsy for human neuromuscular spindle studies and some topics for future work have been suggested.