Abstract
The development and the growth of skeletal muscle were studied on the M. complexus (hatching muscle), the M. biceps femoris and the M. pectoralis superficialis from late embryos and 1, 4 and 14 days old chickens. The M. complexus showed a remarkable growth in the later stages of embryonic development for breaking of the egg shell at the time of hatching and rapidly regres sed in size after hatching. The rapid growth of this muscle was initiated by an increase in both absolute and relative weights at 16 days of incubation and reached its maximum development at 20 days of incubation. Histological measurements on the total cross sectional area and muscle fiber size were made in the M. complexus and other muscles, and indicated that these values paralleled the changes in wet weight and in percentage of body weight. The total number of muscle fibers in the M. complexus reached its maximum at 16 days of incubation and no further significant changes appeared during subsequent stages of development. The remarkable growth of the M. complexus is mainly due to a true hypertrophy.
