250 THE DOG-FISH. 



them back from the sinus venosus, and they will be 

 described in this way, though it must be remembered 

 that the now of blood in them during life is towards 

 the sinus venosus. They are chiefly remarkable for 

 their usually enormous size, the dilated portions 

 being spoken of as sinuses. 



To dissect the veins, slit open the ventral wall of the sinus 

 venosus transversely, and wash out the contained blood; then 

 follow the veins with a seeker, slitting them open along their 

 ventral walls, and washing out the blood. If preferred, they 

 may be injected with plaster of Paris, or they may be inflated 

 with air. 



a. The hepatic sinuses open into the sinus venosus by 



a pair of apertures in its posterior wall close to 

 the median plane and near the dorsal surface. 

 The apertures lead into a pair of wide sinuses, 

 separated from each other by an imperfect 

 septum, and lying immediately behind the peri- 

 cardium, between it and the liver, and ventral to 

 the oesophagus. 



Slit open one of the hepatic sinuses, and follow it back 

 into the corresponding lobe of the liver, noting its large size 

 and the numerous veins opening into it. 



b. The Cuvierian sinuses are a pair of rather narrow 



tubes, forming lateral continuations of the sinus 

 venosus, the wall of the pericardium marking 

 the boundary between the two. Each is about a 

 quarter of an inch long, and curves upwards from 

 the sinus venosus round the side of the oesophagus, 

 lying in a notch in the posterior border of the 

 fifth cerato -branchial cartilage. Each Cuvierian 

 sinus receives about the middle of its course the 

 inferior jugular sinus, and at its dorsal end the 

 great anterior and posterior cardinal sinuses. 



i. The inferior jugular sinus, which is of small 

 size, can be traced forwards and inwards 



