CHAP, x ARTERIES 451 



gills, and from it arise on either side paired lateral 

 branches, the afferent branchial arteries (Fig. 119, a. br. a, 

 and compare Fig. no). Each afferent artery passes to 

 the corresponding gill, and there branches out into 

 smaller and smaller arteries, which finally open into a 

 network of delicate capillaries (p. 95), with which the 

 connective-tissue of the branchial filaments is permeated. 

 The blood in these respiratory capillaries is therefore 

 brought into close relation with the surrounding water, 

 and as the blood flows through them it exchanges its 

 carbon dioxide for oxygen, obtained from the air dissolved 

 in the surrounding water. 



From the respiratory capillaries the blood is collected 

 into minute arteries which join into larger and larger 

 trunks, and finally unite into efferent branchial arteries 

 (e. br. a) by which the purified blood is carried from the 

 gills. The efferent arteries of the right and left sides 

 communicate with a median longitudinal artery, the 

 dorsal aorta (d. ao), which passes backwards, immediately 

 beneath the vertebral column, to the end of the tail. 



From the efferent branchial arteries and the dorsal 

 aorta are given off numerous arteries supplying the 

 various parts with blood. The most important of these 

 are paired carotid arteries (c. a) to the head, and sub- 

 clavians (scL a] to the pectoral fins ; unpaired splanchnic 

 arteries (cl. a, ms. a) to the enteric canal, liver, pancreas, 

 and spleen ; numerous paired renals (r. a) to the 

 kidneys, spermatic (sp. a) or ovarian arteries to the 

 gonads, and a pair of iliacs (il. a) to the pelvic fins. 

 The posterior part of the dorsal aorta, supplying the 

 tail, is contained in the haemal canal of the caudal verte- 

 brae, and is often spoken of as the caudal artery (cd. a). 



The arrangement of the arteries in the tadpole is very 

 similar to that described above, and the diagram (Fig. 119) 

 would serve almost equally well for a tadpole as for a fish. 



F F 2 



