. Chordate morphology. Morphology (Animals); Chordata. external carotid ductus caroticus common carotid stem. pulmonary artery ' A 2 mm B 3 mm C mm D 6 mm E mm Figure 11-8. Five stages in tiie development of the aortic arches of man. (After Kramer, 1942) internal carotid 3 4 6 truncus of valves in the truncus is not apparent. From these rows of valves the four ridges observed in the higher forms devel- oped and made possible the subdivision of the truncus. THE AORTIC ARCHES Mammals The pharynx of the mammal in the course of its develop- ment produces a series of branchial pouches. Thes
. Chordate morphology. Morphology (Animals); Chordata. external carotid ductus caroticus common carotid stem. pulmonary artery ' A 2 mm B 3 mm C mm D 6 mm E mm Figure 11-8. Five stages in tiie development of the aortic arches of man. (After Kramer, 1942) internal carotid 3 4 6 truncus of valves in the truncus is not apparent. From these rows of valves the four ridges observed in the higher forms devel- oped and made possible the subdivision of the truncus. THE AORTIC ARCHES Mammals The pharynx of the mammal in the course of its develop- ment produces a series of branchial pouches. These pouches do not break through to the exterior, but they do resemble the pouches which give rise to the gill clefts in fishes. Re- lated to these pouches are a series of arteries, the aortic arches. These connect the ventral aortic trunk (ventral aorta) with the dorsal posteriorly conducting trunk (dorsal aorta) or trunks (radices aortarum). In development the first arch is followed shortly by the second (Figure 11-8). The arches lead into separate dorsal radices which further posteriorly fuse and form the midline dorsal aorta. The third and fourth arches now appear, while the first and second arches undergo reduction. By the time the sixth arch has appeared, the first and second are greatly reduced. The third and fourth arches are large, the fifth very small (Figure 11-9). The sixth sends a posterior branch back to the lungs and connects with the dorsal aorta by a ductus arteriosus (ductus Botalli). The first and second arches disappear, and their basal stem becomes the external carotid (Figure 11-10). The. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Jollie, Malcolm. New York, Reinhold
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