The author describes the behavior of the circulatory system of sea snakes when they are removed from the ocean (see lines 17-29) primarily in order to
-illustrate what would occur in the circulatory system of terrestrial snakes without adaptations that enable them to regulate theri blood pressure in vertical orientations
-explain why ardoreal snakes in vertical orientations must rely on musclecontractiond to restore blood pressure to the brian
-illustrate the effects of circulatiry failure on the behavior of arboreal snakes
-illustrate the superiority of the citculatory system of the terrestrial snake to that of the sea snake