Sea-fisheries laboratory. 229 



after traversing the systemic capillaries, returns 

 through three main channels. The blood from the 

 head returns directly to the sinus venosus by the 

 jugular veins, but two portal circulations are interposed 

 in the course of the blood returning from the viscera and 

 the body. The caudal vein, the genital veins and other 

 smaller vessels convey blood returning from the great 

 muscles of the trunk and from the reproductive organs to 

 the kidneys, where these afferent veins break up into a 

 network of capillaries, which are in close association with 

 the renal tubules. From the kidney the blood leaches 

 the heart again via the two ductus Cuvieri, or precaval 

 veins ; the blood from the stomach, intestine and spleen, 

 containing the absorbed products of digestion, is conveyed 

 to the liver by several afferent vessels known as the hepatic 

 portal veins, and after traversing the hepatic capillaries 

 enters the sinus venosus by the hepatic veins. 



The Pericardium and Heart. — The pericardial cavity 

 [Per. fig. 20) is displayed by dissecting away the pectoral 

 girdles with their muscle masses, which cover it laterally 

 and in front ; behind, it is bounded by a strong fibrous 

 septum which separates it from the body cavity. Its walls 

 contain black pigment. The heart, which nearly fills its 

 cavity, is suspended by the hepatic veins traversing its 

 posterior wall, by the ductus Cuvieri above, and by the 

 bulbus arteriosus in front. It lies in a curved position, so 

 that the sinus and auricle are nearly vertical, the ventricle 

 oblique and the bulbus nearly horizontal. 



The Cuvierian Ducts or precaval veins ( V. pc. fig. 22) 

 are wide thin-walled vessels passing slightly obliquely 

 over the lateral surfaces of the oesophagus. Their union 

 beneath the latter forms the sinus venosus (Sin. V. figs. 

 21 and 22). Sinus and precaval veins together form a 

 horse-shoe shaped chamber surrounding the oesophagus 



