422 



CHORD AT A, 



In the skate the blood from the heart passes by a 

 ventral aorta to the gills by five afferent branchials, and 

 thence by five efferent branchials to the dorsal aorta. 

 There are in fishes never less than four branchials. 

 When the gills are lost in terrestrial animals the afiferents 

 become directly continuous with the efferents, and the 

 arches so formed are called arterial arches. 



Fig. 303. — Lateral Views of Anterior Arterial System of 

 Vertebrates. 



Carotid. Efferent Branchial: 



Afferent Afferent Branchial Artery. 



Branchials. Branchials. 



Carotid. 



Dorsal Aorta. 



3 4 Afferent Branchials. 



A, Skate. B, Teleostome, 



Dorsal Aorta. 

 /_ 



4 Pulmoi 



In the frog there are four arterial arches at an early stage, 

 but later the first remains as the ca7'otld arch, the second 

 persists as the systemic, the third is said to atrophy, and the 

 fourth forms the pulmonary. The connections between 

 these arches persist as membranous vestiges called ductus 

 Botalli. 



In reptiles much the same arrangement holds, but in 

 birds the left systemic is lost, whilst in mammals the right 

 atrophies. 



In the venous system the principal change is the replace- 

 ment in vertebrates above fishes of the paired cardinals by 



