202 



is in Ceratodus a purely secondary arraogement, occurring at a very 

 late stage in development. 



b) The anterior carotid arteries of Ceratodus and of Amphibia 

 are exactly homologous up to a late stage of development. The 

 carotid arteries of the adult Ceratodus, however, are not equivalent 

 to those of any other known form. 



c) The anterior carotid artery of Ceratodus does not represent 

 as has been supposed, the combined pseudobranchial and anterior 

 carotid arteries of such forms as Mustelus and Raja, but rather re- 

 presents the posterior carotid artery of the Elasmobranchs. There is 

 considerable similarity between the anterior carotid arteries of Cera- 

 todus and Callorhynchus. 



d) The posterior carotid artery of Ceratodus is derived partly 

 from a portion of the original anterior carotid and does not represent 

 a carotid comparable with that of any other known form. 



A further point of similarity between Ceratodus and the Amphibia 

 is seen in the presence of a lingual artery and the mode of its 

 development {I. Fig. I C). This is exactly similar to the lingual or 

 "external carotid" artery of such forms as Rana and Triton. 



Primarily the blood is returned from the region of the yolk and 

 developing gut through the single ventral vitello-intestinal vein opening 

 into the sinus venosus (s.i. Fig. 1 A). The anterior or vitelline portion 

 of this vein enlarges, separates from the posterior our subintestinal 

 portion and becomes the hepatic vein of the young fish {h. Fig. 1). 

 An hepatic-portal vein develops independently upon the dorsal side 

 of the intestine {h.p. Fig. 1 B) and rapidly grows down around it to 

 a mid-ventral position where it unites with the subintestinal vein {h.p. 

 Fig. 1 C) the anterior portion of which has disappeared. The primitive 

 vitello-intestinal trunk therefore becomes in part the hepatic veins and 

 in part a portion of the hepatic-portal of the adult. Ceratodus finds 

 its closest agreement here among the Urodela where one of the 

 usually paired vitello-intestinal veins is greatly reduced, and in some 

 of which the hepatic-portal vein is similarly formed. 



Lateral cutaneous veins (I.e. Fig. 1) accompanying the sense 

 organs of the lateral line develop just as in the Amphibia and have 

 adult relations similar to those of the Elasmobranchs and Amphibia. 

 The abdominal vein of Ceratodus (a. Fig. 1 C) develops as a pair of 

 small vessels opening into the sinus venosus laterally, precisely as in 

 Amphibia. They pass backward accompanying the ventro-lateral rows 

 of integumentary sense organs, bearing to them a relation similar to 

 that which the lateral cutaneous veins bear to the lateral line organs. 



