338 ANATOMICAL TECHNOLOGY. 



Ventriculus sinister. — It is easier to defer the examination of 

 the left auricle until after the simpler ventricle has been opened. 



With the scalpel, make a longitudinal incision through the 

 lateral wall about midway of the width of the ventricle. This will 

 permit a view of the cavity without injuring the massive columnse 

 carnese which will generally appear one at either side. Then make 

 a transverse incision at right angles with the basal end of the first, 

 making sure that it is on the ventricular side of the furrow between 

 the auricle and the ventricle. With the scalpel, remove the enclosed 

 angles of the wall on either side so as to expose the cavity as much 

 as desirable. Note that one of the wide Mcuspid valves is applied 

 against the septum so as to conceal the orifice of the aorta. 



§ 902. Aorta. — Pass the scissors blade behind the septal bicuspid 

 valve into the aorta and slit it up. The incision will probably cut 

 through one of the three semilunar valves. Note (A) the position of 

 these valves, dorsal, dextral and sinistral ; (B) the corresponding 

 sinuses of Valsalva ; (C) the orifices of the right and left cardiac 

 arteries from the dextral and sinistral sinuses. 



Farther peripherad, note (A) the origins of the lyrachio-cephaliG 

 and left subclavian arteries ; (B) in some cases, at the opposite side 

 of the aorta from those vessels, a slight depression indicating the 

 place of attachment of the ductus arteriosus. 



§ 903. Auricula sinistra. — Returning to the left ventricle, pass 

 the probe into the left auricle and ascertain the points of attach- 

 ment of the pulmonary veins nearest the appendix. Then intro- 

 duce a scissors blade and divide the parts fi'om the ventricle just 

 dorsad of the appendix, carefully avoiding the veins just mentioned. 



Slit up the appendix to its tip. Then with the probe, seek out 

 the orifices of the three groups of pulmonary veins as represented 

 in Fig. 91. Cut along the auriculo-ventricular furrow so as to per- 

 mit a better view of the cavity. Note the more or less marked 

 crescentic fold which indicates the dorsal margin of the/ossa ovalis. 

 Hold the septum between the eye and the light and note its thin- 

 ness at that place. Examine the right side of the septum for the 

 fossa and the left for the crescentic fold (§ 868). 



FROZEN SECTIONS OP THE THORAX. 



§ 904 Figures 99 and 100 represent respectively ttie caudal and cephalic aspects of a 

 frozen transection of the thorax, the thickness of the section being a trifle over 1 cm. The 

 manner of preparation has been described in g 324. 



