ANATOMY IN A NUTSHELL. 



241 



heart. Its walls are one-third as thick as those of the left ventricle, and it 

 holds about three ounces. Its posterior surface rests upon the Diaphragm 

 forming a small part of the back of the heart, while its anterior surface forms 

 most of the front of the heart. 



1. The conus arteriosus or infundibulum is a conical pouch at the upper 

 and left angle of the ventricle, from which the pulmonary artery arises. 



2. The auriculo-ventrieular opening has been described with the auricle. 



3. The opening of the pulmonary artery which lies at the summit of the 

 infundibulum is circular. It is guarded by the pulmonary semilunar valves. 



4. The tricuspid valve consists of three portions. The largest of these 

 segments, called the left or infundibular flap, lies at the left and front of the 

 opening. The right flap is to the front and right, while the third, called the 

 posterior or septal flap, is posteriorly. The center of each of these flaps is thick, 

 the lateral margins are thin. 



5. The chorda? tendinae are fibrous cords which are attached to the mar- 



PLATE XCVII. 



A, ARTIC.WVTH 

 U^t? ANT. ARCH 0FA7LA5. 



BODY. 



Anterior View of Axis. 



gins and ventricular surfaces of each of these flaps. Three or four are attached 

 t<> the liases of each flap and are continuous with the fibrous ring which surrounds 

 the auriculo-ventrieular opening. Four to six pass to the central part of these 

 flaps, and the finest and most numerous go to the free margins of these flaps. 



6. Column;? earneae project from the walls of the ventricle except near the 

 pulmonary opening. They are divided into three sets, the first set are at- 

 tached throughout their length thus forming mere ridges. The second sel called 

 trabecular, are attached to their ends only, thus forming arches, while the third 

 3e1 . <;tlled musculi papillares, are attached to one end only, thus forming pillars. 

 These musculi papillares are two in number, an anterior and a posterior, and 

 they give attachment by their free ends to the chor.hr tendinae. Those from 

 the anterior one pass to the right and left flaps, while those from the posterior 

 one pass to the right and septal flaps. A few of the chordae tendinae pass to 

 the left and septal flaps from the septum. 



7. The semilunar valves (Plate XCXXX.) (pulmonary) are three in num- 

 ber. Two anterior, (a righl and left), and one posterior. They are formed by 



