THORAX AND ABDOMEN OF THE HORSE 29 



A. CORONARIA DEXTRA. — As will be seen later, the right coronary^ 

 artery leaves the aorta behind the cranial semilunar valve at the origin 

 of this vessel from the left ventricle. The first part of its course is 

 cranial in direction, but it soon bends towards the right, and then 

 sweeps in a caudal direction along the right part of the coronary groove. 

 A descending branch (ramus descendens) follows the right longitudinal 

 groove of the heart to within a measurable distance of the apex, 



A. CORONARIA SINISTRA. — The left coronary artery leaves the aorta 

 behind the left caudal semilunar valve and passes backwards to the 

 right of the pulmonary artery. Its circumflex branch (ramus circum- 

 flexa) follows the coronary groove to near the caudal border of the 

 heart, and ends close to the termination of the right coronary artery. 

 Numerous branches ramify over the surface of the left ventricle, but the 

 largest (ramus descendens) leaves the parent vessel close to the 

 pulmonary artery and runs down the left longitudinal groove. 



V. CORDIS MAGNA. — The great cardiac vein begins near the apex of 

 the heart as a companion of the descending branch of the left coronary 

 artery. It accompanies the artery as far as the coronary groove, then 

 turns at a right angle to follow the groove along the left side and round 

 the caudal border of the heart, and ends by opening into the coronary 

 sinus" (sinus coronarius), a short but wide vessel that will be found 

 ventral to the termination of the caudal vena cava. 



V. CORDIS MEDIA. — The middle cardiac vein lies in the right lontyi- 

 tudinal groove in company with the descending branch of the right 

 coronary artery. Its mode of termination is variable. In the majorit}'^ 

 of subjects it pours its blood into the coronary sinus ; but not in- 

 frequently it opens independently into the right atrium. 



Vv. CORDIS MINORES. — Four or five small veins drain the surface of 

 the right atrium and ventricle, and enter the right lialf of the coronary 

 groove to end finally in the depressions between the pectinate muscles 

 on the inner surface of the wall of the right atrium. 



Dissection. — Now proceed to examine the interior of the cavities of 

 the heart, beginning with the right atrium. To open this cavity most 

 advantageously two incisions are necessary : (1) Enter the knife at the 

 termination of the caudal vena cava and carry it in a straight line to 

 the point at which the cranial vena cava joins the heart. (2) From the 

 middle of the first incision carry a second to the tip of the auricle of 

 the atrium. 



It is well not to depart from the instructions laid down for opening 

 the various cavities of the heart, as the incisions have been planned to 

 give the maximum of exposure of the interior with the minimum of 

 damage. 



' Corona [L.], a crown, something crown-Uke or encircling. 



- (Sinus [L.], a curved surface, a curve ; in a borrowed sense, the bosom, a cavitv. 



