Practicum V. The Right Auricle. 31 



peripheral end is probably tied ; it will be more fully seen upon dis- 

 section. 



d. On the ventral aspect, between the two auricles, is the promi- 

 nent PULMONARY ARTERY, extending from the base of the RIGHT VEN- 

 TRICLE obliquely sinistro-cephalad. The part of the ventricle from which 

 the artery springs is the CONUS. 



e. The AQRTA, with its principal branch (B) will be seen more dis- 

 tinctly at a later stage. 



5. The Sulcus Terminalis. The right auricle presents two regions, one smooth, be- 

 tween the attachments of the postcava and precava, the other corrugated slightly, extend- 

 ing dextrad toward the pulmonary artery. Between the two areas is a slight furrow which 

 begins at the notch at the dextro-cephalic corner of the auricle and crosses diagonally to 

 the sinistro-caudal angle. This furrow, more distinct in man, is the sulcus terminalis of 

 His ; the two regions of the auricle are the ATRIUM and the APPENDIX. 



6. Dissection of the Heart. The order of dissection follows the 

 course of the blood through the organ. Bear in mind that, although an- 

 atcunically united, and acting together as muscles, as to their cavities, the 

 right and lejt sides of the heart are entirely separated by complete partitions 

 between the two auricles and between the two ventricles. Physiologically, 

 between the right ventricle and the left auricle, intervene the lungs ; in 

 like manner between the left ventricle and the right 'auricle, intervene 

 all the other parts of the body, including the substance of the heart itself ; 

 see Anatomical Technology, Fig. 92. 



a. If the directions are followed closely and carefully, the dissected 

 heart may be wortli keeping as a guide in future dissections. 



7. Opening the Right Auricle. a. Hold the heart with its ventral 

 side toward you, as on PI. XII. At the dextro-cephalic angle of the ap- 

 pendix, 5-10 mm. from the margin, push in a scissors-point. Cut thence 

 caudad and then sinistrad, keeping at about the same distance from the 

 margin, to a point about midway between the right margin and the per- 

 icardial line where it crosses the postcava. 



b. Lift the edge of the flap and note the wide mouths of the POST- 

 CAVA and PRECAVA, separated by a prominent ridge ; PI. XIII, 9. 



c. Cut carefully almost to the pericardia! line ; thence, clearing the 

 ridge just mentioned and another at the opposite side of the precaval 

 orifice, cut to the point of departure. 



8. The Coronary Sinus. The large orifice of this is seen just 

 caudad of that of the postcava, PI. XIII. Slit its ectal wall for 1-2 cm. 



a. Extending obliquely cephalad from the sinus is the (left) AZYGOUS 

 VEIN ; with the scissors slit it to its cut (or tied) end (PI. XII, Az.), noting 

 its semi-circular course. 



b. Near the angle of the appendical part of the left auricle is the 

 large orifice of the CARDIAC (coronary) VEIN, bringing blood from the sub- 

 stance of the heart ; it is seen transected in PL XIV. 



c. Between the cardiac vein and the orifice of the sinus are several 

 small openings, the FORAMINA OF THEBESIUS, the mouths of small veins. 



d. With the scissors remove the free portions of the walls of the 

 atrium, postcava and precava. Compare PL XIII ; note one or two 

 Thebesian foramina where the precava becomes continuous with the 

 atrium. 



9. Opening the Right Ventricle. This must be done very carefully, 

 especially if a permanent preparation is to be made. 



a. On the ventral aspect of the heart (PL XII) note the line of at- 

 tachment of the pulmonary artery, the heart being darker and firmer than 



