VASCULAR SYSTEM 



251 



together of the epibranchial vessels to form the dorsal aorta, the 

 pc. 



mcs 



hr. 



of? 



Fin. '220. 



Branchial circulation of Cemtotlit* (from Spencer's figures). I-V, live branchial slits; abr, 

 anterior efferent vessel ; a.c, anterior carotid ; f 3-6, four afferent vessels (corresponding to 

 the original arches *) ; c, conns ; cl, coeliac artery ; d, ductus Cuvieri ; eb '>-, second and fourth 

 epibranchial arteries; h.a, hyoid artery (from original 2nd arch); /,, air-bladder ; La, lingual 

 artery; mes, mesentric artery; p.a, pulmonary artery; pin; posterior efferent vessel; p.c, 

 posterior cardinal; p.v, pulmonary vein; $, position of closed spiracle ; v.a, ventral artery; 

 v.c, vena cava inferior. The gills are represented on the hyoid and next 4 branchial arches. 



CCL 



ma,, 



vatf. 



Fio. 221. 



Branchial circulation of Protopterits (from Parker's figures). a/2-6, afferent branchial 

 arteries ; nf.g, afferent vessel to external gill ; ca, carotid ; cl, coeliac artery ; c.t, left branch of 

 dorsal aorta formed by .junction of branchial efferent vessels ; d, ductus Cuvieri ; ef.g, efferent 

 vessel of external gill ; e.y, external gill ; ep, epibranchial region of arterial arch of first gill-less 

 branchial arch ; ep.h, epibranchial vessel of hyoid arch ; ht, heart ; L, lung ; m.a, median 

 artery ; p.a, pulmonary artery ; p.v, pulmonary vein ; v.ao, ventral aorta ; v.c, vena cava 

 posterior. The five branchial slits are shaded ; the first two branchial arches are without gills. 

 A dotted line indicates the position of the obliterated spiracle. 



structure of the conus, and the position of the auricles, are features 

 in which they distinctly approach the Amphibia. 



The aortic arches of the first two gill-less branchial bars of the 



