APPENDIX. 215 



b. Slit open the auricular appendage; note the fleshy projections 

 (columnce carnece) on its interior, and the general smoothness of the 

 rest of the inner wall of the auricle. Notice the columnce car new 

 over the inner surface of the ventricular wall, also the considerable 

 thickness of the latter, as compared with that of the right ventricle or 

 of either of the auricles. 



c. Carefully raise the wedge-shaped flap of the left ventricle, and 

 cut on towards the base of the heart, until the valve (mitral) between 

 auricle and ventricle is brought into view; one of its two flaps will 

 be seen to lie between the auriculo- ventricular opening and the origin 

 of the aorta. 



Examine in these flaps their texture, the chorda? tendineae, the 

 columns carneae, etc., as in the case of the right side of the heart (12). 



d. Examine the semilunar valves at the exit of the aorta; then 

 cutting up carefully between two of them, examine the bit of aorta 

 still left attached to the heart, and note the valves more carefully as 

 described in 12. d. Note the origins of the coronary arteries in two 

 of the three dilatations (sinuses of Valsalva) of the aortic wall above 

 the semilunar flaps. 



14. Examine a piece of aorta. Note that when empty it does not 

 collapse; the thickness of its wall ; its extensibility in all directions; 

 its elasticity. 



15. Compare with the artery the thin- walled flabby veins which 

 open into the heart. 



