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, however, must also be taken into account in evaluating the results. The macroscopic appearances of the upper and lower parts of the artery suggested the presence of a larger amount of elastic tissue in the lower, appearances analogous to those in the carotid of the ostrich (Dr Beattie). The comparative histology of the two portions, given in detail below and illustrated by microphotographs, amply corroborates these suggestions.
