200 Mammalia, 



yeins cross over by an * innominate ' vein to form, with the 

 corresponding vessels on the right side, one vena cava superior. 



Examination of Lungs and Heart. The Lungs 

 will be seen to be freely suspended in the Pleural 

 cavity, and to bear no marks of the ribs, &c., on their 

 exterior. They are made up of five lobes, of which some are 

 apportioned to the right and some to the left section of the 

 organ, according as they are supplied from the right or left 

 primary branch of the pulmonary artery. In this specimen 

 four lobes enter into the composition of the right Lung ; the 

 fourth lobe being in the middle line in relation with the 

 apex of the heart above, and the left Phrenic nerve on its left ; 

 this lobe, in excess of the three-lobed constituents of the right 

 Lung in Man, is termed the post-caval lobe, as being notched 

 on its dorsal surface for the passage of the inferior cava, 

 after it has pierced the diaphragm en route to the Heart. 



Between the post-caval lobe and the left Lung, dorsad of the 

 left Phrenic nerve, the student will readily perceive the 

 (Esophagus with the Pneumogastric nerve lying on it, which, 

 after piercing the diaphragm, continues forward dorsad of the 

 root of the left Lung. Further he will note the anterior 

 margin of the left Limg, and of the anterior lobe of the right 

 Lung to be indented by the descending cava of each side ; 

 that of the left side passing ventrad of the root of the left 

 Lung, and winding round the left contour of the Heart to 

 reach the back of the right ventricle. The two descending 

 cavse thus enclose in their grasp the roots of all the vessels 

 leaving the heart. 



The root of the Lung will be seen to consist, on its ventral 

 aspect, of the vessels proceeding between the Lungs and the 

 Heart, viz., the pulmonary arteries and veins ; dorsad of 

 these, and hidden by them, are the air tubes or Bronchi, which 

 by their union, as will be shown presently, form the Trachea : 

 dorsad of the Bronchi, as may be seen by lifting up the left 



