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 larvae. 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; /, //, 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. 



