. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Internal I 'ransportation 365 The usual embryonic arrangement of these branchial arterial vessels, as indicated in Figure 301, may be taken as a point of departure for the adaptations to follow in the different vertebrate classes. It will be seen that the branchial loops do not connect directly with the main dorsal aorta but first join with two smaller blood vessels, the radices aortae, which secondarily join, like the converging arms of the letter T, to m
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Internal I 'ransportation 365 The usual embryonic arrangement of these branchial arterial vessels, as indicated in Figure 301, may be taken as a point of departure for the adaptations to follow in the different vertebrate classes. It will be seen that the branchial loops do not connect directly with the main dorsal aorta but first join with two smaller blood vessels, the radices aortae, which secondarily join, like the converging arms of the letter T, to make the single dorsal aorta. m HE Dorsal Aorta— Fig. 301. Theoretical plan of embryonic arterial loops. (After Boas.) Infernal Carotid ""External Carotid -Gill Region. Ventral Aorta -- Radix Aortae Subclavian Dorsal Aorta Fig. 302. Plan of arterial loops in fishes. In fishes (Fig. 302), the two most anterior pairs of loops, that are sup- ported by the mandibular and hyoid arches of the splanchnocranium, are reduced to branches of the third in adult life, leaving the remaining four to become the branchial arches, interrupted by the capillaries of the internal gills as they pass from the ventral side to the radices aortae. In urodele amphibians (Fig. 303) external gills are introduced which, unlike the internal gills of fishes, do not directly interrupt the branchial loops but are established on a detour from the loops (Fig. 328), so that it is possible for the blood to pass from the ventral to the dorsal aorta by either of two routes, one through the uninterrupted branchial loop in which no capillaries are present, and the other by way of a side line through the capillaries of the external gills. Three pairs of such external gills, situated on loops IV, V, and VI. may be present in urodeles. Thus in those salamanders that discard their. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - colorat
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