The incidence of tail flexion to the left side in mouse embryos.

The tail was flexed towards the left side of the body in 5.2 and 6.2% of ICR mouse embryos at 10.5 and 11.5 days of gestation respectively. Body weights of these embryos did not differ from their littermates with right-sided tail flexion. The flexion to the left may be an easily detectable parameter of variation in the morphology of mouse embryos at midgestation.