85 
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 reaches 
the heart again va the two ductis Cuvieri, er 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 ducttis 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. pe. fig. 22) 
are wide thin-walled vessels passing slightly obliquely 
over the lateral surfaces of the esophagus. 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 cesophagus 
