80 ELEMENTARY PHYSIOLOGY. XV. 



water onwards. The water will mount in the tube con- 

 nected with the artery, and will only descend a little 

 way on unclasping the india-rubber tubing. Pour water 

 into the long glass tube by means of a funnel, and ob- 

 serve the column of water which the semilunar valves 

 will sustain. Note the distension of the arterial walls 

 and the bulging at the attachment of the valves. When 

 the pressure of the column of fluid is removed the artery 

 by its elasticity returns to its previous dimensions. 



3. Repeat the above observation with the pulmonary 

 veins and aorta. 



4. Compare the united sectional areas of the superior 

 and inferior venae cavae when distended, with the area 

 of the aorta below the origin of the innominate artery. 



5. Having removed the tubes, lay open the superior 

 and inferior venae cavae, and bring the incisions to meet 

 in the front of the auricle. Note 



The size and form of the auricular cavity. The auricu- 

 lar appendage with its muscular fretwork. 



The septum auricularum. 



The fossa ovalis, or expression of the foetal foramen 

 ovale, which is early closed by the growth of the septum 

 auricularum. 



The Eustachian valve, a slightly projecting membra- 

 nous fold, immediately beneath the entrance of the in- 

 ferior vena cava, and again beneath this 



The opening of the comparatively large left azygos 

 vein. 



The auriculo-ventricular orifice. 



6. Cut open longitudinally the azygos vein, and 



