STRUCTURE OF THE HEART. 



137 



to the pulmonary artery, d; e,f, the tricuspid valve : e is placed on the 

 anterior curtain, and/* on the right curtain ; #, the long columna carnea, 

 to the apex of which the anterior and right curtains of the tricuspid 

 valve are connected by the chordaa tendineas; h, the long moderator 

 band ; i, the two columnse carneaa of the right curtain ; &, the attach- 

 ment by chorda3 tendinea3 of the left limb of the anterior curtain ; I, I, 

 chorda3 tendinese of the fixed curtain of the valve ; m, the valve of the 

 pulmonary artery : the letter of reference is placed on the inferior semi- 

 lunar segment ; n, the apex of the right appendix auriculas ; o, the left 

 ventricle ; JP, the ascending aorta ; #, its arch, with the three arterial 

 trunks which arise from the arch ; r, the descending aorta. 



Fig. 59 exhibits the view of the organ on its left side. Like the pre- 

 Fig 59 ceding, the figure and description 



are from Dr. Wilson. 1, cavity 

 of the left auricle : the number 

 is placed on that portion of the 

 septum auricularum correspond- 

 i n g Tftifa the centre of the fossa 

 ovalis ; 2, cavity of the appendix 

 auriculas ; 3, opening of the two 

 right pulmonary veins ; 4, the 

 sinus into which the left pulmo- 

 nary veins open ; 5, the left pul- 

 monary veins ; 6, the auriculo- 

 ventricular opening; 7, the coro- 

 nary vein, lying in the auriculo-ventricular groove ; 8, the left ventricle ; 

 9, 9, the cavity of the left ventricle. The numbers rest on the septum 

 ventriculorum. a, the mitral valve : its flaps are connected by chordaa 

 tendineas to , , b, the columnaa carneaa ; c, c, fixed columnas carneae, form- 

 ing part of the internal surface of the ventricle ; d, the arch of the aorta, 

 from the summit of which the three arterial trunks of the head and up- 

 per extremities are seen arising ; -0, the pulmonary artery ; f, the oblit- 

 erated ductus arteriosus ; g, the left pulmonary artery ; A, the right ven- 

 tricle ; i, the point of the appendix of the right auricle. 



Externally, the heart is covered by a serous membrane, pericardium, 



and in its interior is sheathed by the 

 endocardium, an extension of the inte- 

 rior coat of the great blood-vessels. 

 Though its movements are wholly in- 

 voluntary, its muscular fibres are of the 

 transversely striated kind. They are 

 about one third less in diameter than 

 Muscular fibres of the heart. those of voluntary muscles generally, 



Human heart on the left side. 



