Differential Blood Flow Through the Afferent Branchial Arteries of the Skate, Raja Rhina*

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Abstract
1. In Raja rhina the entire cardiac output is distributed to the afferent branchial arteries by two stem arteries on each side. In each of nine skates (1.5 to 7.5 kg.) the total blood flow to gills on one side was measured simultaneously by means of two electromagnetic flow probes implanted on the stem arteries. 2. At rest the average cardiac output was about 21 ml/kg. min. and blood flow was distributed almost equally to the anterior and posterior stem arteries. 3. During short periods of free swimming the proportion of blood flow through the posterior stem invariably increased. This increase is apparently correlated with increased water flow past these gills during swimming. 4. It is postulated that the selective change of blood flow with short exercise is caused by a decrease of vascular resistance of the posterior gills. 5. The data are discussed in relation to the bottom-living habits of skates and the alternate pathways of the respiratory water current through the spiracles at rest and through the mouth and spiracles during swimming. Comparisons are made with other elasmobranchs in regard to the configuration of the branchial vessels in relation to probable patterns of water flow past their gills.

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