CIRCULATORY SYSTEM. 



501 



which passes both in and out under the operculum. 



The gill filaments borne on 

 the four anterior branchial 

 arches are long triangular 

 processes, whose free ends 

 form a double row. As there 

 are no partitions between 

 the five gill clefts, the fila- 

 ments project freely into the 

 cavity covered by the oper- 

 culum. Along each arch and 

 filament there are blood 

 vessels, bringing the impure 

 blood, and removing it puri- 

 fied. On the internal surface 

 of the operculum lies a red 

 patch, the pseudobranch or 

 rudimentary hyoidean gill. 



The swim bladder lies 

 along the dorsal wall of the 

 abdomen ; the duct which 

 originally connected it with 

 the gut has been closed. 

 The dorsal wall of the 

 bladder is so thin, that the 

 kidneys and vertebras are 

 seen through it ; the ventral 

 wall is thick, and bears 

 anteriorly a large vascular 

 rete mirabile, which receives 

 blood from the mesenteric 

 artery and returns blood to 

 the portal vein. 



Fig. 169. — Diagram of 

 Teleostean circulation. (After 



NUHN.) 



The venous system is dark. A.^ 

 auricle; V., ventricle; b.a., bulbus 

 arteriosus; 7'.a., ventral aorta; a.l>r., 

 atTerent branchials ; e.br., efferent 

 branchials ; c.c.^ cephalic circle ; c, 

 carotids ; A.c.v., anterior cardinal veins ; 

 P.C.y., posterior cardinal veins; d.c, 

 ductus Cuvierii ; li.a.^ dorsal aorta ; c.v., 

 caudal vein ; c.a., caudal artery ; k., 

 kidney. 



Circulatory System. 



The heart lies within a peri- 

 cardial chamber, separated by 

 a partition from the abdo- 

 minal cavity. The blood from 

 the body and liver enters 

 the heart by the sinus venosus, passes into the thin-walled 



