VENOUS SYSTEM 227 



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^Jollow it back 



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



und 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 



along the outer wall of the pericardial cavity ; 



and then forwards, in the floor of the mouth, 



ventral to the gill-arches. 



Eio, 50. — Seyllium canicula. Dissection of the venous system from the 

 ventral surface. The right half of the lower jaw, the right lobe 

 of the liver, and the alimentary canal from the oesophagus back- 

 wards have been removed, (a. m. m.) 



A, nostril. AS, anterior cardinal sinus. B, right olfactory organ. 

 BV, subclavian vein. Cj left half of lower jaw. D, fifth nerve crossing the 

 orbit. DC, Cuvierian sinus. E, right eye. F, cut edge of floor of mouth. 

 Q-, first branchial cleft. H, ventricle. HS, left hepatic sinus. HV, left 

 hepatic vein, I, auricle. JV, left inferior jugular sinus. JV, opening 

 of right inferior jugular sinus into sinus venosus. K, pericardial cavity. 

 L, left lobe of liver. LV, right lateral vein. M, oesophagus, cut across. 

 M V, hyoidean sinus. K", kidney or metanephros. O, communication between 

 the right and left posterior cardinal sinuses. OS, orbital sinus. P, post- 

 orbital sinus. PS, posterior cardinal sinus. PV, posterior cardinal vein. 

 RS, apertures of renal veins] into posterior cardinal veins. SA, aperture 

 from sinus venosus to auricle. SV, sinus venosus. ^ 



<J 2 



