182 OUTLINES OF CHORDATE DEVELOPMENT 



When the internal gills disappear, during metamorphosis, the 

 lower end of the efferent branchial artery (original aortic arch) 

 reacquires a direct connection with the afferent branchial artery 



ap 



ao 



FIG. 66. Diagrams of the branchial blood vessels in frog larvse. After 

 Marshall. A. Of a 7 mm. larva (shortly after hatching). The vessels supplying 

 the external gills are removed, only their roots being indicated. B. Of a 12 mm. 

 tadpole. The vascular loops in the gills are omitted, a, Auricle; ac, anterior 

 (internal) carotid artery; am, anterior commissural artery; ao, dorsal aorta; ap, 

 anterior palatine artery; b, basilar artery; c, anterior cerebral artery; eg, carotid 

 gland; cv, posterior (inferior) vena cava; dC, ductus Cuvieri; g, pronephric 

 glomerulus; h, hepatic veins; hy, hyoidean vein; I, lingual artery; m, mandibular 

 vein; p, pulmonary artery; ph, pharyngeal artery; pm, origin of posterior oom- 

 missural artery; pp, posterior palatine artery; pv, pulmonary vein; s, vein of 

 oral sucker; t, truncus arteriosus; u, cutaneous artery; v, ventricle; 1-4, first to 

 fourth afferent branchial arteries; I, II, efferent arteries of the mandibular and 

 hyoid arches; III-VI, first to fourth efferent branchial arteries; VII, lacunar 

 vessel of the fourth branchial arch. 



and the blood again passes directly from the truncus to the 

 dorsal aorta (Fig. 65, A], This connection enlarges as the gill 

 capillaries diminish, and finally these direct paths remain as 

 the only vessels of the branchial arches. 



