DISSECTION OF THE HEART. .337 



Instruments and Materials. — Sharp Charri^re scalpel ; coarse 

 or medium curved scissors ; silver probe, syringotome or dull 

 tracer ; 15 per cent, glycerin ; a heart, the larger the better, with the 

 pericardium removed. The dissection may be done upon a fresh 

 specimen or upon one simply hardened in alcohol ; it is easier, 

 however, if the organ has been distended and hardened with alco- 

 hol (§ 842). 



§ 899. Auricula dextra. — Pinch up with the forceps a bit of the 

 lateral wall of the right auricle, for example, just dorsad of the 

 appendix, and remove it with the scissors. Introduce the probe 

 and ascertain the points of emergence of the postcatia and prcBcava. 

 With the scissors, remove the entire lateral wall, including that of 

 the appendix, but leave the attachments of the cavse. 



Note (A) the smoothness of the ental surface of the sinus as com- 

 pared with the fretwork in the appendix ; (B) close to the auriculo- 

 ventricular furrow, just caudad of the postcava, the orifice of the 

 sinus coronalis (§ 877), guarded by the valva Thebesii (§ 883). 



§ 900. Ventriculus dexter. — Pass the probe through the orifi- 

 cium auriculo-ventriculare into the right ventricle, noting that no 

 obstruction is oflfered by the tricuspid valves. Ascertain by prob- 

 ing the limit of the ventricular cavity, and with the scalpel make a 

 V-shaped flap having its base at the base of the ventricle and 

 including the entire lateral wall. 



Turn this flap toward the auricle and note : (A) the two or three 

 columncB carnecd ; (B) the smaller trabeculcB, both fleshy and ten- 

 dinous ; (0) the chordae tendinese passing from the columns or 

 directly from the ventricular wall to the borders of the three vaUoB 

 tficuspides ; (D) that two of these valves (dorsal and ventral) will 

 be moved by the lifting of the flap ; the third (septal) is applied 

 closely to the septum, and its chordae are very short, arising either 

 from the septum directly or from very slight elevations. 



§ 901. Conus arteriosus and A. pulmonalis. — Pass the probe 

 sinistro-cephalad through the conus into the artery. Then introduce 

 a scissors blade in the same direction and slit both up along the most 

 prominent part of the convexity. On divaricating the sides, it wiU 

 be found that the incision has either divided the ventral semilunar 

 valve or gone between it and the dextral. Note (A) the three valves ; 

 (B) the corresponding sinuses of Yalsalva; (0) the bifurcation of 

 the A,. pulmonalis into right and left branches to the corresponding 



lungs. 



32 



