THE BKANCHIAL BLOOD-VESSELS. 



173 



gill arch as a double row of branching tufts, ventral to the 

 external gill. Capillary loops soon appear in these tufts, form- 

 ing a series of capillary connections between the afferent and 

 efferent branchial vessels, . similar to those in the external gill, 

 but situated more ventrally. At the same time the external 

 gill diminishes considerably in size. 



The next change of importance is the establishment of a 



EF.3 EFi 



VD AF.4. 



FIG. 80. Diagrammatic figure of the head of a ]2 mm. Tadpole from the 

 right side, showing the heart and branchial blood-vessels. The capillary 

 loops of the gills are omitted, x 33. 



A, aorta. AB, basilar artery. AF-1, AF.2, AF.4, afferent branchial vessels of 

 first, second, anil fourth branchial arches. AL, lingual artery. AP, pulmonary artery. 

 AR, anterior cerebral artery. AS, posterior palatine artery. AT, anterior palatinp 

 artery. ATT, cutaneous artery. AY, pharyngeal artery. CA, anterior cornmissnral 

 vessel, seen in section. CGr, bulb-like ililatatioii on the lingual artery. OP, posterior 

 commissural vessel, seen in section. EF.l, EF.2, EF-3, EF.4, efferent branchial 

 vessels of first, second, third, and fourth branchial arches. QM, glorneralus. RA, right 

 auricle. RB, left auricle. RT, truncus arteriosus. RV, ventricle. VD, Cuvierian 

 vein. VH, hepatic vein. VI, posterior vena cava. VP, pulmonary vein. 



direct connection between the afferent and efferent branchial 

 vessels. The two vessels (Figs. 77 and 79, AF.I and EF.l) lie 

 alongside each other in the arch, the afferent being the posterior 

 of the two. In tadpoles of about 12 mm. length, in which the 

 sucker is disappearing, and the hind limbs are present as a pair 

 of small rounded papillae at the base of the tail, a direct com- 

 munication is established between the ventral ends of the 



