Through the courtesy of Dr Chalmers Mitchell and Dr Vevers, and the facilities kindly afforded by Dr Scott and Dr Beattie, one of us had recently the opportunity of examining the carotid artery of a young giraffe at the Zoological Gardens. The object in view was to find out what structural mechanism existed for overcoming hydrostatic pressure in blood vessels, and the neck vessels of the giraffe seemed most likely to give the answer. The intermittent output of the heart,