BLOOD-VASCULAR SYSTEM OF THE TILE-FISH. 107 



I. THE HEPATIC PORTAL SYSTEM. 



The arrangement in the abdomen of the veins which form the hepatic portal 

 vein is not at all constant. The order generally met with will lie described. 



At the base of the liver two main trunks {',1. 50) enter the large transverse 

 hepatic portal vein (Ifi) which distributes the blood through the liver. The larger 

 of these two trunks (jl) is formed by the union of the following vessels: (a) Branches 

 from the rectum and distal portion of the intestine {49); (b) branches from the distal 

 loop of the intestine (4-7) (principally from its left side); (c) a gastric branch ( i6) 

 from the caecal portion of the stomach; (d) a vein (45) from the spleen and distal 

 loop of the intestine (principally right side) which joins the trunk opposite the right 

 side of the stomach; (e) the small pancreatic vein (44)i an d a large vein (43) which 

 leaves the ventral surface of the swim-bladder and returns the blood of the rete 

 mirabile; and finally (f) a vein from the oesophagus (42) which joins the trunk just 

 before it enters the liver. The second trunk, which helps to form the portal vein (50), 

 returns blood to the liver from the greater part of the proximal loop of the intes- 

 tine (52), and from the stomach by several gastric branches (51); it also, at times, 

 receives branches from the distal loop of the intestine. 



II. VEINS OPENING INTO THE SINUS VEXOSUS. 



A. The hepatic veins (2), which are two in number, leave the right and left seg- 

 ments of the liver, one on each side of the median line, and empty immediately into 

 the sinus venosus. 



B. A large vein (4) from each side opens into the ventral surface of the sinus 

 venosus near the Cuvierian duct. This vessel is formed by the union of the follow- 

 ing three veins: (a) The brachial branch (5), which returns blood from the pectoral tin 

 and from the anterior part of the lateral muscles of the abdomen (6); (b) a vessel (7), 

 which returns blood from the ventral tin and adjacent muscles, and (c) a vein (8), 

 which returns blood from the thyroid gland and muscles ventral to the ventral aorta. 

 Sometimes this latter vein (8) unites with its fellow of the opposite side by a small 

 trunk (9) just below the ventral aorta. These three veins (-7. 7, and 8) run close to 

 the pericardium and, after uniting to form a single vessel on each side of the heart, 

 open into the sinus venosus, as described above. 



C. The Cuvierian ducts (S) open into the lateral extremities of the sinus venosus. 

 They are two large vessels, about 2.5 cm. in length, situated on each side of the 

 (esophagus just behind the fifth branchial arch. 



III. THE VEINS OPENING INTO THE CUVIERIAN DUCTS. 



A. The inferior jugular vein (10), a large single vessel, its cranial end situated 

 in the median line, returns blood from the lower jaw and floor of the mouth, dust 

 caudal to the hypohyal, it receives two veins (11), one from each side, which return 

 blood from the branchiostegal and ceratohyal regions, and, continuing caudad just 

 dorsal to the ventral aorta, it curves to the right of the heart, close to the pericar- 

 dium, and opens into the right Cuvierian duct near its junction with the sinus 

 venosus. 



