Abstract
The purpose of this study is to investigate histologically the distribution of muscle spindles and the relationship (size, number) between intrafusal and extrafusal fibers. M.tibialis ant. of Wistar-strain rats was chiefly used in this experiment. Alcohol solution of Sudan black B was used to stain the fibers. The results were as follows: (1) Muscle spindles were distributed more at the middle part of the muscle and were observed more in innermost region than in peripheral. (2) Muscle spindle consists of sarcosome rich (red) and sarcosome poor (white) intrafusal fibers. The number of red intrafusal fibers involved in a muscle spindle is more than that of white intrafusal fibers. (3) Development of intrafusal fibers and extrafusal fibers was observed as days passing after birth. The rate of hypertrophy of extrafusal fibers is greater than that of intrafusal fibers while their development occurs.
