. Chordate morphology. Morphology (Animals); Chordata. ductus arteriosus now connects the pulmonary artery with the dorsal stem. In the tadpole the development of the aortic arch, in terms of both external and internal gills, can be observed (Figure 11-15). Choanate fishes Among the dipnoans there are four or five aortic arches leading away from the heart: the second, third, fourth, fifth, and sixth in Prolopterus (Figure 11-16). The arches bearing gill filaments are fish-like with afferent and efferent divisions (Figure 11-17). The artery to the lung arises dorsally from the common efferent c
. Chordate morphology. Morphology (Animals); Chordata. ductus arteriosus now connects the pulmonary artery with the dorsal stem. In the tadpole the development of the aortic arch, in terms of both external and internal gills, can be observed (Figure 11-15). Choanate fishes Among the dipnoans there are four or five aortic arches leading away from the heart: the second, third, fourth, fifth, and sixth in Prolopterus (Figure 11-16). The arches bearing gill filaments are fish-like with afferent and efferent divisions (Figure 11-17). The artery to the lung arises dorsally from the common efferent channel (radix aortae). The first three arches have a common ventral stem as do the fifth and sixth arches. Neoceratodus lacks the second efferent vessel but is otherwise similar (Figure 11-17). Latimeria has not been described, but, on the basis of the lungfishes, is probably like the actinopterygian. Actinopterygian fishes Among the actinopterygian fishes, there are four pairs of branchial arches arising from a ventral aorta. These are arches 3 to 6 of the pairs observed in the embryo of higher vertebrates (Figure 11-18). They are associated with five gill openings derived from pharyngeal pouches. Each arch is broken into an afferent division taking blood to the fila- ments and an efferent division collecting blood from the filaments and carrying it to the dorsal aorta (Figure 11-19). In the primitive fishes, Polypterus and Amia, there is a pulmonary artery leading from the sixth eflFerent vessel on either side back to the swim bladder. This pulmonary artery has the same association observed in the choanate fishes. In most actinopterygians, the dorsal aorta supplies the swim bladder (Figures 9-31, 9-32). In Acipenser or Lepisosteus, the second afferent arch is pre- sent and serves the hyoid hemibranch (Figure 9-35). The spiracular, or mandibular hemibranch, is served by the ef- ferent vessel of the hyoid hemibranch and the efferent vessel of the first branchial arch (3). In th
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