138 



THE COMMON FROG. 



[chap. 



The gill veins pour their contents into branchial 

 veins, one of which ascends the outer side of each 

 branchial arch, increasing in size as it ascends. The 

 branchial veins open into the great dorsal aorta, 

 whence the blood is distributed over the body. 

 Generally the branchial arteries are only connected 

 with the branchial veins by the intervention of the 



Fig. 8i. — Infero-lateral view of Head and Aortic Arches oi Lepidosiren (after Hyrtl). 

 a, oesophagus ; b, anterior end of bulbus aortse ; c, common roots of the first 

 aortic arches ; d, third aortic arch ; e, first aortic arch ; f, dorsal union of the 

 first three aortic arches ■,ff, aorta ; h, coeHac artery ; /, exit of the fifth nerve ',k, part 

 of operculum ; /, exit of the nervus vagus from the skull ; m, branches to oeso- 

 phagus ; 71, nerve going to the rectus abdominis : o, nervus lateralis ; /, first and 

 hypertrophied rib ; q, posterior part of the skull ; r, segmented neural spines ; 

 s, chorda dorsalis ; t, mandible ; u, quadrate. 



capillary vessels of the gills. Sometimes, however 

 (as e.g. in the mud-fish, Lepidosircn) the branchial 

 veins are directly continuous with the branchial 

 arteries. 



In the tadpole, while the gills remain fully de- 

 veloped, a condition exists quite similar to that of 



