THE EIGHT VENTRICLE 



623 



■ . Although called a fossa, it is usually a deep but narrow diverticulum in the horse The 

 interatrial septum is very thm here, and in some cases the foramen ovale faUs to close entirely. 



The Right Ventricle 

 The right ventricle (Ventriculus dexter) constitutes the right-anterior part of 

 the ventricular mass. It forms almost all of the anterior border of the heart, but 

 does not reach the apex, which is formed entirely by the left ventricle. It extends 

 from the third rib to the fourth intercostal space on the left side, to the fifth inter- 

 costal space on the right side. It is somewhat triangular in outline, and is crescentic 

 in cross-section. Its base is connected largely with the right atrium, with which it 



Pulmonary veins 



/A. 



Anterior 

 vena cava 



MusculiLS _.- 

 ■pectinatus 



Right coronary 

 artery 



Tricuspid valve 

 Chordae tendui 



Great coronary 

 ,vein 

 ^,, ' Left coronary 

 Bf| _, artery {circum- 

 '♦ 7 ' flex branch) 

 -^'r-'" Bicuspid valve 



, Chorda, tendinece 



Musculus 

 papillaris 



Moderator band 



,-- Left ventricle 



Moderator bated --'^'^ 



Right ventricle '' 



Right coronary arttry ■' 



Fig. 547. — Section of Heakt of Hokse. 

 Specimen hardened in situ and cut nearly at right angles to the ventricular septum. The left ventricle is contracted, 

 but not ad maximum. F. a., Segment of aortic valve. 



communicates through the right atrio- ventricular orifice; but its left part projects 

 higher and forms the conus arteriosus, from which the pulmonary artery arises. 

 Its apex is two inches or more (ca. 5-6 cm.) above the apex of the heart. On 

 opening the cavity it is seen that the atrio-ventricular orifice and the cavity of the 

 conus arteriosus are separated by a thick rounded ridge (Crista supraventricularis). 

 The axis of the cavity, taken from this ridge to the apex, forms a spiral curve down- 

 ward and to the right. The septal wall is convex and faces obliquely forward and 

 to the right. 



The right atrio-ventricular orifice (Ostium atrio-ventriculare dextrum) is oval 

 and is chiefly opposite to the fourth and fifth ribs and the intervening space. ^ The 

 plane of the opening is oblique, much lower in front than behind. 



^The extent of the atrio-ventricular orifices, of course, varies with the phase in which the heart 

 is fixed. In subjects which are preserved by intravascular injection of formalin solution the right 

 side of the heart is usually in diastole, while the left side is more'or less contracted. 



