176 Anatomy of the Rabbit. 



(b) The pulmonary artery (a. pulmonalis) leaves the base of the 

 right ventricle, passing forward and to the left in a some- 

 what spiral fashion around the aorta. On the dorsal sur- 

 face of the latter it divides into the right and left pulmonary 

 arteries, one for each lung. At the point of division the 

 pulmonary artery is connected with the aorta by a short 

 fibrous cord, the arterial ligament (lig. arteriosum), repre- 

 senting the foetal connection of the two vessels through the' 

 ductus arteriosus (p. 44). 



(c) The left coronary artery (a. coronaria sinistra) passes back- 

 ward on the ventral surface of the heart, lying in the anterior 

 longitudinal sulcus. A corresponding right coronary artery 

 (a. coronaria dextra) passes to the right side of the heart, 

 lying between the right ventricle and the right atrium. 



The two vessels supply the substance of the heart. They are the 

 first branches of the aorta, arising from the aortic sinuses at its base. 



(d) The left atrium (atrium sinistrum) is the thin-walled chamber 

 lying to the left at the base of the heart. The pulmonary 

 veins (venae pulmonales), several on either side, enter the 

 left atrium, passing from the medial portions of the lungs. 



(e) The right atrium (atrium dextrum) resembles the left in the 

 . character of its wall. It receives the right and left superior 



caval and the unpaired inferior caval veins. 



The heart may be removed by dividing the great bloodvessels. The 

 arch of the aorta should be removed with the heart by dividing the 

 vessel at a point beyond the origin of the left subclavian, and then 

 severing the carotids and subclavians at their bases. This exposes the 

 surface for the subsequent examination of the posterior end of the 

 trachea and its connections with the lungs. 



Open the right ventricle by a longitudinal incision of the ventral 

 wall, extending the incision forward into the pulmonary artery; also 

 both atria by transverse incisions. By washing out the cavities, 

 the internal features of the wall, including the arrangement of the 

 valvular structures, may be examined as follows: 



In the right ventricle : 



(a) The trabeculae carneae; muscular ridges of the internal sur- 

 face of the wall. 



(b) The tricuspid valve (valvula tricuspidalis). The thin 

 membranous flaps composing the valve enclose the atrio- 

 ventricular aperture, and project into the cavity of the 

 ventricle. Their margins, which are otherwise free, are con- 

 nected by slender fibrous cords, the chordae tendineae, with 

 the papillary muscles (mm. J papillares), the latter being thick 

 muscular projections, of somewhat conical shape, arising 

 from the opposite walls. 



(c) The semilunar valves (valvulae semilunares) of the pulmonary 

 artery are three extremely thin folds guarding the entrance 

 to the vessel from the right ventricle. Two of the valves 



