VASCULAR SYSTEM 339 



carotid artery, eventually enters the cranial cavity and sub- 

 divides into anterior and posterior cerebral arteries for the brain, 

 also giving off a branch which unites with its fellow of the 

 opposite side directly behind the infundibulum. A posterior 

 carotid springs from the epibranchial of the first branchial arch 

 and divides into palatine, orbital, and ocular branches ; and from 

 the ventral end of the anterior efferent vessel of the second 

 branchial arch is derived a hypobranchial artery for the heart 

 and pericardium. The pulmonary arteries for the lung-like air- 

 bladder have their origin from the fourth pair of epibranchial 

 arteries. 



As in so many other details of its anatomy, Neoceratodus 

 exhibits in its arterial system abundant evidence of the wide- 

 spreading affinities of the group to which it belongs. In its 

 branchial arterial system Neoceratodtis presents a singular com- 

 bination of features which, individually, are characteristic of 

 Amphibia and Elasmobranchs. Special Amphibian features may 

 be noted in the origin of the afferent branchial arteries almost 

 simultaneously from the anterior end of the conus arteriosus ; 

 in the mode of union of the epibranchial arteries to form 

 the dorsal aortae ; in the origin of a lingual artery from the 

 efferent vessel of the first branchial arch ; and in the derivation 

 on either side of a pulmonary artery from the fourth epibranchial 

 artery. Agreement with Elasmobranchs is to be found in the 

 presence of two efferent branchial vessels in each branchial arch, 

 although the relations of these arteries are more primitive than 

 in most adult Elasmobranchs, inasmuch as the two efferent vessels 

 of the same arch unite to form an epibranchial artery ; and also 

 in the origin and distribution of the anterior and posterior 

 carotids. Lastly may be mentioned the fact that Neoceratodus 

 agrees not only with the AmpMbia but also with those generalised 

 Teleostomi, Polypterus and Amia, in the mode of origin of the 

 great arteries for the air-bladder. 



Of the two remaining Dipnoi, the arterial system of Proto- 

 pterus ^ is better known than that of Zepidosiren, but in both 

 cases further research is needed before a satisfactory comparison 

 can be made with Neoceratodus and other Vertebrates. It is 

 evident, nevertheless, that both genera differ from Neoceratodus 

 in approximating more closely to the Amphibia than to the 

 1 Newton Parker, Trans. Roy. Irish Acad. xxx. 1892, p. 173. 



