THE BEANCHIAL 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 



VD AFA. RB Wv 



Fig. 80.— Diagrammatic figure of the head of a 12 mm. Tadpole from the 

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

 loops of the gills are omitted, x 35. 



A,- aorta. AB, basilar artery. AF-l, AF.2, AP.4, afferent branchial vessels ui 

 first, second, and fourth brancllial arches. AXj, lingual artery, AP, pulmonary artery. 

 AK, anterior cerebral ai"tery. AS, posterior palatine artery. £^^ anterior palatine 

 artery. AIT, cutaneous arterj^-rAY, pharjmgeal artery. C A, anterior commissural 

 vessel, seen in section. C(3> bulb-like dilatation on the lingual artery. CP, posterior 

 commissiural vessel, seen in section. EP.l, EF.2, EF.3. EF.4, efferent branchial 

 vessels of first, second, third, and fourth branchial ai-che-s. G-M, glomer ulus. RA, right 

 auricle. RB, left auricle. RT, truucus arteriosus. RV, ventricle. VD, Cuvieriaii 

 vein. VH, hepatic veiji. VI, posterior vena cava. VP, pulmonai-y vein. 



direct connection between the afferent and efferent branchial 

 vessels. The two vessels (Figs. 77 and 79, af.i and ef.i) 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 j^resent 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 



