XII 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 eoceratodus 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 Amphibia 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 
eases further research is needed before a satisfactory comparison 
can be made with Weoceratodus 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. 178. 
