422 CHORDATA. 
In the skate the blood from the heart passes by | 
ventral aorta to the gills by five afferent branchials, anc 
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 afferent 
become directly continuous with the efferents, and th 
arches so formed are called arterial arches. 
Fig. 303.— LATERAL VIEWS OF ANTERIOR ARTERIAL SYSTEM O 
VERTEBRATES. 
Carotid. Efferent Branchials. Dorsal Aorta. 
£\Xs L 
A 
z —— 
Afferent Afferent Branchial Artery. 
Branchials. Branchials. 
4 Dorsal Aorta. 
Carotid. 2 3 4 Dorsal Aorta, 
Cc 
3 
g 
7 S) Systemic 2 3 4 Pulm 
TH 32 3 4 Afferent Branchials. 
A, Skate. B, Teleostome. C, Frog. 
In the frog there are four arterial arches at an early stage 
but later the first remains as the carotid arch, the secon 
persists as the sys¢emc, the third is said to atrophy, and th 
fourth forms the pu/monary. The connections betwee 
these arches persist as membranous vestiges called ductu 
Botalui. 
In reptiles much the same arrangement holds, but i 
birds the left systemic is lost, whilst in mammals the rigl 
atrophies. 
In the venous system the principal change is the replaci 
ment in vertebrates above fishes of the paved cardinals b 
