DISSECTION Off A BONY FISH. 13 



the pectoral fins nearly to the isthmus, taking care as before 

 not to cut the underlying parts. Cut away the thin parti- 

 tion (false diaphragm) just in front of the liver. This will 

 lay open the pericardial cavity (part of the coelom). 



In the pericardial cavity lies the heart. It consists of a 

 triangular ventricle below (in the normal position of the 

 fish) and a more dorsal auricle. In front the ventricle gives 

 off a blood-vessel, which at first has a conical enlargement 

 (arterial bulb), and then is continued forward as the ven- 

 tral aorta. Behind the heart is a blood-cavity (venous 

 sinus) extending across the body-cavity in front of the false 

 diaphragm. How are the hepatic veins (p. 12) related to 

 this? 



Inject the blood-system by inserting the canula of an 

 injecting syringe (see Appendix) in the arterial bulb and 

 forcing some colored fluid * forward through the ventral 

 aorta. After the injection follow the ventral aorta forward, 

 tracing its branches (afferent branchial arteries) into the 

 gill-arches (p. 11). What relations do these branchial 

 arteries and ventral aorta bear to the pharynx ? 



Now cut away the floor of the throat and trace in the 

 gill-arches the efferent branchial arteries to their union 

 above the gullet in the longitudinal blood-vessel, the dorsal 

 aorta. Can you find this aorta in the roof of the peritoneal 

 cavity ? Could the blood-system, so far as you have studied 

 it, be described as two longitudinal vessels lying on either 

 side of the alimentary canal, and connected by a series of 

 paired transverse vessels ? What must be the course of the 

 blood in the different parts of the system ? Draw a dia- 

 gram illustrating the relations of the circulatory apparatus 

 to the alimentary canal and gill-slits. 



* None of the gelatine mixtures answer well here, as the necessary 

 heat weakens the walls of the blood-vessels. 



