336 AMPHIBIA xn. 19 



right side of the ventricle and may thus receive first the venous blood. 

 The conus arteriosus has transverse and longitudinal valves. 



The ventral aorta is very short and the arches much modified in the 

 adult (Fig. 198). Of the original six that can be recognized the first 



Ophth 



A a . abdom 



Ailiaca comm 

 A.epiy.-ves 



A. ischiadica 



Fig. 199. Diagram to show the chief arteries and 

 their anastomoses in the frog. (After Gaupp.) 



two disappear, the third on each side gives rise to the carotid artery, 

 the fourth remains complete and forms the systemic arch. The fifth 

 remains also in some urodeles, but disappears in anurans. The sixth 

 arch becomes the pulmonary artery and loses its connexion with the 

 dorsal aorta: special 'cutaneous arteries' carry de-oxygenated blood 

 from this arch to the skin (Fig. 199). These pulmonary arches prob- 

 ably offer a lesser resistance than do the systemic and carotid ones; 

 the pressure in the latter is said to be increased by a special network, 

 the 'carotid gland', though it may well be that this organ is a receptor, 



