1. Blair, D. M., and Davies, F. (1935). J. Anat., Lond., 69, 303.
2. Davies, F. (1930). Ibid., 64, 129 and 319; and (1931), 65, 339.
3. and E. T. B. Francis (1941). Phil. Trans. Roy. Soc., B,, No. 578, 231, 99.
4. and E. T. B. Francis (1941). J. Physiol., 100, 329.