It is not our intention to provide in one place a com­prehensive description of all the blood vessels.

Few things would be more tedious, and there seems to be a pragmatic advantage in fragmenting the account: dealing with the vascularization of particular organs and regions in other chapters makes it is easier to emphasize those features that have a special functional importance or clinical interest. Even so, it is advisable to have an outline of the arterial and venous trees. Because species differences are numerous and would, if given attention, require many qualifications of the description, the dog is used as model; only a few most salient comparative features are noted.