VENOUS SYSTEM. 249 



ventral to the auricle, and forming the most 



conspicuous part of the heart. 

 d. The conus arteriosus is a cylindrical tube, running 



forwards from the ventricle to the anterior end 



of the pericardial cavity. 

 3. The pericardio-peritoneal canal is a median passage, 

 about an inch long, opening in front into the hinder 

 end of the pericardial cavity dorsal to the sinus 

 venosus, and running backwards along the ventral 

 surface of the oesophagus, to open behind into the 

 abdominal cavity. Its anterior opening is large and 

 conspicuous ; the opening into the abdominal cavity, 

 which may be double, is smaller and slit-like. 



Find the pericardial opening in the middle line, imme- 

 diately dorsal to the sinus venosus. Insert a seeker, and pass 

 it davn the canal into the abdominal cavity. 



B. The Venous System. 



The venous system of the dog-fish consists of three great 

 divisions : (1) the veins opening into the sinus venosus, which 

 return blood from all parts of the body to the heart ; (2) the 

 hepatic portal system, which conveys to the liver the blood 

 from the alimentary canal, pancreas, and spleen ; (3) the renal 

 portal system, which conveys to the kidneys the blood from 

 the part of the body behind the cloaca. 



1. The veins opening into the sinus venosus. 



These veins are most readily traced by following 



Fig. 52. Scyllium 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 backwards 

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



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

 subclavian vein. C, left half of lower jaw. D, fifth nerve and buccal branch 

 of seventh nerve crossing the orbit. DC, Cuvierian sinus. E, right eye. f, cut 

 edge of floor of mouth. G , first branchial clef t. H, ventricle. HS, left hepatic 

 sinus. HV, left hepatic vein. |, auricle. JV, left inferior jugular sinus. 

 JV', opening of right inferior jugular sinus into Cuvierian sinus. K, pericardial 

 cavity. L, left lobe of liver. |_V, right lateral vein, m, oesophagus, cut across. 

 MV, hyoidean sinus. N, 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, aper- 

 tures of renal veins into posterior cardinal veins. SA, aperture from sinus 

 venosus to auricle. SV, sinus venosus. 



