. Elements of Comparative Anatomy. 582 COMPAEATIVE a,r various arrangements. For example, there is a muscular process, which is able to partly shut off the cavity which gives off the branchial arteries from the rest of the ventricular cavity. The ventricle is com- pletely divided in the Crocodilini. The membranous valves of the ostium atrio-ventriculare are greatly developed in the right half of the heart. In the Crocodilini there is only one of these valves on the right side, and it extends along the septum of the ventricle; the other valve is replaced by a process of the lateral mu
. Elements of Comparative Anatomy. 582 COMPAEATIVE a,r various arrangements. For example, there is a muscular process, which is able to partly shut off the cavity which gives off the branchial arteries from the rest of the ventricular cavity. The ventricle is com- pletely divided in the Crocodilini. The membranous valves of the ostium atrio-ventriculare are greatly developed in the right half of the heart. In the Crocodilini there is only one of these valves on the right side, and it extends along the septum of the ventricle; the other valve is replaced by a process of the lateral muscular wall of this chamber. The arterial bulb, which is single ex- ternally, is apparently given off from the right ventricle. It is, however, divided into a series of canals, which are connected with both ventricles. There are pouched valves at the root of the arteries. Of the five primitive arterial arches, the two first have disappeared, and the rest undergo various metamorphoses in the different divisions. In the Saurii the third persists on both sides, and is connected on the right with the fourth arch, which, like the two branches of the third arch, is given off from the vessel that arises from the left ventricle. The left half of the fourth arch is connected with the third arch on its own side, and so corresponds to the right ventricle. The fifth arch on either side is partly converted into the pulmonary arteries, which primitively spring from it only, and which are given off from the trunk of the pulmonary artery in consequence of the differentation of the primitive aortic bulb. There are, there- fore, two aortic arches on either side, one of which, the second on the left, conveys venous blood. It is, however, connected peri- pherally with the other arches, so that the two kinds of blood must be mixed. In the Ophidii the first pair of arches that persists in the Saurii is not generally connected with the second pair, but the continuation of this portion is converted in
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Keywords: ., bo, bookcentury1800, bookdecade1870, bookpublisherlondonmacmillan
