. Elements of Comparative Anatomy. 580 COMPAEATIVE Pig. 327. Aortic arches of paradox a. a Trunk of the branchial arteries. 12 3 Arterial arches; the first two are united to form the aorta, p Pulmonary artery. b Ductus Botalli. hr Branchial clefts. h/ Accessory gill. ao Aorta. c Coeliac artery, oe CEsophagus (after Hyrtl). example of this, for it is in them that the cavities of the heart are first divided. In Lepidosiren a network of muscular bands is continued from the wall of the auricle right through it, and forms a kind of partition. The auricle is thereby divided i
. Elements of Comparative Anatomy. 580 COMPAEATIVE Pig. 327. Aortic arches of paradox a. a Trunk of the branchial arteries. 12 3 Arterial arches; the first two are united to form the aorta, p Pulmonary artery. b Ductus Botalli. hr Branchial clefts. h/ Accessory gill. ao Aorta. c Coeliac artery, oe CEsophagus (after Hyrtl). example of this, for it is in them that the cavities of the heart are first divided. In Lepidosiren a network of muscular bands is continued from the wall of the auricle right through it, and forms a kind of partition. The auricle is thereby divided into a right and left portion, but there are many points by which these two parts communicate with one another, and they also open by a common opening into the ventricle. The venous sinus now opens into the right side of the auricle, and a pulmonary vein passes into the left side. The ventricle, also, is partly divided by muscular processes; and, in correspon- dence with this, the lumen of the arterial bulb is divided into two cavities, each of which gives rise to special arteries. These form three vessels which extend along the anterior branchial arches; the most anterior on either side is connected with the second one, and unites with its fellow of the opposite side to form an aorta {ao). These two vessels have no relation to the gills. The third arch gives rise to branchial arches, but it is also connected by a narrow duct {b) with the root of the aorta, and it is continued on as the pulmonary artery {p). This arch forms, therefore, a branchio-pulmonary artery, and the two anterior arches, as they do not give ofE any branchial vessels, represent aortic arches. The circulatory apparatus of the Amphibia presents the same conditions. In most, the auricle is completely divided, but in some, as in Proteus, it is not so; in Salamandra, also, there is a hole in the septum. The systemic veins open into the right, the pulmonary into the left auricle. The ventricle is single, and there
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