140 PRACTICAL ZOOLOGY. 



which is stretched a paler membrane ; by slight pres- 

 sure with the handle of the forceps, prove that this 

 membrane is thin and yielding. Below the fossa ova- 

 lis is the opening of the afcygos vein. With a 

 syringe inject water into it and find whence it comes. 

 The projection between the entrance of this vein 

 and the fossa ovalis is the Eustachian valve. With 

 scissors slit open the azygos vein and find, entering 

 it, veins from the walls of the heart. Trace these 

 veins. 



3. Cut away the whole of the right auricle; hold the 

 heart in the left hand, with the left ventricle resting 

 against the palm ; pour water suddenly from a consid- 

 erable height into the right ventricle, watching closely 

 to see the valves float up and separate the auricle 

 from the ventricle. Pour in water again, and as soon 

 as the valves rise, press with the fingers on the outside 

 of the right ventricle ; note the effect of this pressure. 

 Where does the water escape ? 



4. Empty the heart and examine the valves which have 

 been seen ; they will now be found lying close against 

 the walls of the ventricle. Note the white cords 

 attached to the lower edges of these valves. 



5. Push a finger pasfrthese valves to the very bottom of 

 the ventricle ; from the outside cut through the wall 

 of the ventricle at this point, and cut cautiously 

 upward along the border of the cavity of the right 

 ventricle. Raise the outer wall of the ventricle and 

 more thoroughly study the valves ; slip a blunt instru- 

 ment between the flaps of the valves and the walls 

 to which they adhere, and raise them so they can be 

 better seen. How many flaps are there, and how are 



