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 \\c\\ of Head and Aortic Arches q^ Lepid^siren (after Hyrt! . 

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

 aortic arche-- ; d, th rd aortic ar^h ; e, first aortic arch ; f^ dorsal union of tlie 

 first three aortic arches ; ,f, porta ; //, coeliac artery ; /, exit of the fifth nerve ; k, part 

 of opercu uni ; /, txil of the nervus vagus from the skull ; ;«, branches to ceso- 

 phasius ; n, nerve going to the rectus abdominis : o, nervus lateralis ; /, first and 

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

 s, chorda dorsalis ; t, manoible ; ic, 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 fulV de- 

 veloped, a condition exists quite similar to that of 



