THORAX AND ABDOMEN OF THE HORSE 



33 



The exit from the ventricle, that is, the opening (ostium pulmonale) 

 from the conus arteriosus into the pulmonary artery, is furnished with 

 three pocket-shaped semilunar valves so arranged as to prevent the 

 backward flow of blood from the artery into the ventricle, but offering 

 no obstacle to the passage of blood from the ventricle into the artery. 

 These valves will be more conveniently examined when, at a later stage 

 of the dissection, it is possible to remove the heart from the thorax. 



A. pulmonalis.' 



V. cordis magna. 



Aortic semilunar ■ 

 valves. 



A. coronaria 

 sinistra(ramus 

 descendens). 



Vv. pulmonales. 



;;v— — — Cavity of left 

 atrium. 



sr =• =- — Bicuspid valve. 

 — Chordae tendineat. 



— — Transverse muscle. 



Fig. 14. 



-The heart viewed obliquely from the left and behind, with the 

 interior of the left atrium and left ventricle exposed. 



Dissection. — Now proceed to examine the left side of the heart, 

 beginning with the left atrium. To open this cavity it is necessary to 

 make one incision only, entering the knife far back and cutting forwards 

 to the extremity of the auricular appendage. The incision should be 

 made near the coronary groove, so as to avoid injury to the terminations 

 of the pulmonary veins. 



Atrium sinistrum. — In its external characters the left atrium 

 3 



