332 ME. J. S. BUDGETT ON SOME POINTS IN 



Hyrtl, from the arrangement of the main blood-supply to the external gill, argues 

 that this must be homologous with the pseudobraneh of Acipenser, which has the 

 same structure as the succeeding gills. 



The external gills of larval batrachians are borne upon the first two or three gill- 

 arches, there being to each of these arches an external epidermal gill and an internal, 

 probably endodermal, gill. 



Kerr has shown that in larval Dipnoi which possess external gills there is to each 

 arch an internal, probably endodermal, gill and an external epidermal gill, both being 

 supplied by the same afferent artery. 



It appears probable therefore that in the external gill of the hyoid arch in Polypterus 

 we have not the homologue of the internal endodermal pseudobraneh of Acipenser, 

 but of the external epidermal gill of Dipnoi and Amphibia. 



Moreover there is in Polypterus at the base of the operculum a stout branch from 

 the efferent artery (PL LII. fig. 25, hy.eff.') which runs parallel with the afferent 

 artery. The presence of this branch is suggestive, as indicating the position of the 

 pseudobraneh, corresponding to the pseudobraneh of Acipenser, of which in Polypterus 

 there is no further trace. 



Pollard states that he could find no trace of a connection between the last efferent 

 branchial artery and the dorsal aorta, the blood from the last hemibranch passing only 

 to the air-bladder. Part of the blood from this gill does, however, pass to a branch 

 joining the third efferent artery, which on the right side meets the cceliac artery 

 (br.IV.eff.). The main part of the blood from the hemibranch of the IVth arch 

 passes to the air-bladder on either side and is returned from them by veins passing to 

 the hepatic veins, as shown by Joh. Miiller. The vein on the right side is of great 

 size, corresponding to the size of the right air-bladder, and posteriorly unites 

 with the caudal vein. 



It is difficult to see how these air-bladder veins in Polypterus could get converted 

 into the pulmonary veins in Amphibia. It seems more probable that the great vein 

 of the right air-bladder corresponds to the anterior abdominal vein of Amphibia, 

 though it is notorious that veins frequently make secondary connections. 



The subclavian artery of Polypterus passes outwards dorsal to the vagus and the 

 cceliac and pulmonary arteries, and curving ventralwards gives off, near the pericar- 

 dium, a branch on either side (text-fig. 7, br."). The posterior branch, the brachial, 

 is a stout artery passing to the pectoral fin ; the anterior branch runs dorsally 

 again parallel with the main subclavian, and divides to supply the muscles of the 

 shoulder-girdle (text-fig. 7, br. 1 ). After giving off these two branches, the sub- 

 clavian is continued as a small coronary artery along the sides of the pericardium, 

 at the anterior end of which it passes to the walls of the conus and ventricle (text- 

 fig. 7, br."). 



The blood from the conus and ventricle is returned to the ductus Cuvieri bv a 



