Dissection of Common Rat 203 



arising directly from tlie arch of tlie Aorta, but external to 

 the carotid. The arch of the Aorta will be seen to turn over 

 towards the back and left side, then to cross over a highly- 

 injected vessel, which is the pulmonary artery arising from 

 the right ventricle, and then to disappear dorsad of the left 

 cava, and proceed towards the back-bone. If the cleft between 

 the right auricle and ventricle be looked into, the root of the 

 Aorta will be seen to take origin dorsad of, and rather 

 behind the root of the pulmonary artery. 



Removal of Left Lung. The Left Limg should be now 

 removed by section through its root, and the left descending 

 cava cut across, leaving the Phrenic nerve in situ, and the 

 Pulmonary artery and Aorta untouched. By this means may 

 be seen the intermediate course of the Pneumo- gastric nerve, 

 which will be best traced from the point we left it last, m., 

 where crossing the subclavian artery ; from this point it is 

 readily followed downwards ventrad of the Aorta, almost 

 adhering to the dorsal aspect of the Pulmonary artery, and 

 reaching the Oesophagus at the point where the Trachea 

 comes first into apposition with the (Esophagus, just dorsad 

 of the root of the left Lung. 



By this section, also, may be traced the course of the 

 Aorta, after giving off the left subclavian artery ; at first in 

 close apposition with the left of the Trachea, then of the 

 (Esophagus, and lastly, taking up a position almost dorsad of 

 the Oesophagus, but slightly to the left, in which position it 

 continues its course down the back, in the inter-pleural space 

 ventrad of the spine, until near the Diaphragm, at which 

 point, *as above noted, it is directly dorsad of the Oesophagus. 



It will thus be seen that the Aortic trunk is sinorle, 

 which is a characteristic of all warm-blooded animals ; 

 and secondly, that this single trutik arches over towards the 

 left, encompassing the root of the left Lung, a matter to be 



