330 ANATOMY OF THE RABBIT 



the diaphragm, the posterior mediastinum widens into a thin vertical sheet 

 extending from the dorsal thoracic wall to the internal surface of the sternum 

 (Fig. 112). 



The pericardium should be removed, and the external features 

 of the heart^ and its great vessels examined. These are as follows: 



(a) The posterior, somewhat conical, ventricular portion of the 

 heart. The left ventricle (ventriculus sinister) may be 

 distinguished both by its position and by the more solid 

 character of its wall. The right ventricle (ventriculus 

 dexter) is less muscular, and the wall is readily pressed 

 inward. The line of division is indicated on the ventral 

 surface by a faint depression, the anterior longitudinal 

 sulcus. 



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

 the right ventricle, passing forward and to the left and then 

 dorsad and caudad in a somewhat spiral fashion around the 

 aorta. On the dorsal surface of the latter it divides into 

 the right and left pulmonary arteries, one for each lung. 

 Close to the point of division the left pulmonary artery is 

 connected with the aorta by a short fibrous cord, the 

 arterial ligament (lig. arteriosum), representing the foetal 

 connection of the two vessels through the ductus arteriosus 

 (pp. 114, 118). 



(c) The left coronary artery (a. coronaria sinistra) emerges 

 from between the root of the pulmonary artery and the left 

 atrium and divides into two main branches, one passing 

 backward in or near the anterior longitudinal sulcus, the 

 other ramifying over the left side of the heart. The right 

 coronary artery (a. coronaria dextra) runs ventrad between 

 the pulmonary artery and the right atrium and along the 

 right atrioventricular groove, giving off branches to supply 

 the whole right side of the heart. Both vessels supply the 

 walls of the aorta, of the pulmonary arteries, and of the 



^The heart is relatively small in the rabbit, as in most animals not capable of 

 prolonged severe muscular effort but depending upon hiding for safety. Its 

 weight is given as about 0.003 of that of the body, which may be compared with 

 values of about 0.006 in man and 0.01 in a deer. 



