Development of hindlimb muscle spindles in the marsupial Macropus eugenii (tammar wallaby)

The development of muscle spindles was studied in the hindlimb of pouch young of the marsupial Macropus eugenii (tammar wallaby) from birth to 100 days. Primary myogenesis was evident in hindlimb muscles at birth. Presumptive muscle spindles were identified as early as day 30 postnatally. The intrafusal muscle fibres developed sequentially, to form the full juvenile complement by day 50, followed by development of the periaxial space. The formation of muscle spindles in the marsupial's hindlimb after birth was in contrast to the mainly prenatal development of spindles noted in placental mammals.