PISCES. 165 



(2) A hyoidean artery, running from the middle of the same loop to supply 

 pseudobranch and brain. (3) Small vessels to the floor of the mouth from 

 the ventral ends of the efferent loops. 



The veins are partly regular tubes, partly irregular sinuses, all 

 of which have thin walls. They may be divided into : (1) Sys- 

 temic veins. (2) Portal systems. 



(1) Systemic Veins. The impure blood from the anterior 

 part of the body is brought back on each side by an anterior 

 cardinal sinus running above the gill-clefts to the level of the 

 sinus venosus, where it unites with a much larger posterior 

 cardinal sinus bringing forwards the impure blood from the body 

 behind the pectoral fins. By the union of the anterior and 

 posterior cardinal sinuses on each side a very short Cuvierian 

 sinus is formed, which, after receiving a jugular sinus from the 

 floor of the mouth and pharynx, is merged in the corresponding 

 side of the sinus venosus. 



Factors of Cardinals. An orbital sinus surrounding the eye opens behind 

 into a short post-orbital sinus, which again communicates with the anterior 

 cardinal. A hyoidean sinus opens into the front end of the anterior cardinal. 



The posterior cardinals begin between the kidneys, and each of them, 

 before it unites with the corresponding anterior cardinal, receives a lateral 

 vein from the body-wall, a genital sinus from the gonad, and a subclavian 

 vein from the pectoral fin. 



(2) Portal Systems. Hepatic portal and renal portal systems 

 are present, which respectively supply the liver and kidneys with 

 impure blood. 



Hepatic Portal System. The blood from the abdominal 

 digestive organs and spleen, containing most of the products of 

 digestion, enters the hepatic portal vein, which breaks up into 

 branches in the substance of the liver. This organ returns its 

 impure blood direct to the sinus venosus by means of two hepatic 

 sinuses. 



Renal Portal System. The impure blood of the tail passes 

 into a caudal vein which runs forwards to the posterior ends of 

 the kidneys and divides into right and left renal portal veins, 

 which divide up in the kidneys, from which the blood is returned 

 to the posterior cardinals by numerous small renal veins. 



The capillaries are minute tubes arranged in plexuses, in 

 which the smallest arteries end and the smallest veins begin. 



(II.) The lymphatic system consists of minute spaces, small 

 lymphatic vessels, and large cavities, all containing lymph, 



