LEFT VENTRICLE. 



393 



of the heart, and consists of two parts, a sinus and auricular 

 appendix. The sinus is separated from the right one by the 

 interauricular septum. The appendix is longer, narrower, more 

 serrated than the right one, and constricted at its junction with 

 the sinus. It runs along the left side of the origin of the 

 pulmonary artery, which helps to separate it from the right 

 auricle. 



On laying open the cavity, we find the openings of the pul- 

 monary veins, usually two pairs, one pair on the right, the other 

 on the left of the sinus ; they are not guarded by valves. The 

 remaining opening in the left auricle is the auriculo-ventricular, 

 which occupies the floor, and 



with the left 

 upper margin 



communicates 

 ventricle, its 

 being surrounded by a white 

 tendinous ring. The obliter- 

 ated foramen ovale on the 

 septum is indistinct. The 

 inner surface of this auricle 

 is smoother than that of the 

 other, the musculi pectinati 

 fewer, and confined to the 

 appendix. The appendix 

 communicates with the sinus 

 through a round constricted 

 opening. 



Fig. 151. 



Left side of the heart— laid open. 1, Left ven- 

 tricle ; a a, External wall ; b, Cameae columnse ; 

 c, Moderator band ; d d d. Mitral valve ; d' d'. 

 Chordae tendinese ; 2, Left auricle ; a a, Musculi 

 pectinati ; i, Openings of pulmonary veins. 



LEFT VENTRICLE. 



The blood leaving the left 

 auricle enters the left ventricle, 

 which is conical, and occupies the posterior left region of the 

 heart. It is larger, rounder, and more prominent than the 

 right, extending from the auricle to the apex, which it occupies, 

 projecting lower than the right ventricle. The external wall is 

 much thickep than that of the right side, being thickest in the centre. 

 After death the walls of this cavity remain apart, those of the 

 right collapsing; on laying open the cavity (by an incision close 

 upon the anterior furrow, from the apex to near the origin of the 

 aorta, and another upon the posterior furrow, the two lijeeting at 

 the apex), two openings present themselves, the left auriculo- 

 ventricular and the aortic. . The left auriculo-triLtricular open- 



