Common Rat. I7i 



pericardium, the upper four-fifths of which have been 

 removed. Between the inferior surface of the heart and the 

 diaphragm the fourth lobe of the right lung intervenes 

 posteriorly; and between the apex of the heart and the 

 diaphragm and sternum anteriorly, a process of serous mem- 

 brane entangling lobides of fatty tissue is interposed, and 

 connects thus the apex of the pericardium with the sternum 

 and diaphragm. 



n. Left auricle. 



0. Phrenic nerve lying in relation with the left superior cava 

 and passing down from its origin in the neck, in front of 

 that vessel and between the root of the left luug and the 

 pericardium, and by the side of the fourth lobe of the right 

 lung, to distribute itself in the diaphragm. 



p. Aorta. A bristle has been passed between it and the left 

 azygos vein, and abuts on the diaphragm where the left 

 phrenic nerve enters it. Behind this bristle are seen from 

 behind forwards, firstly, the third lobe of the right lung ; 

 secondly, the oesophagus, which is seen to be of a small 

 size in correlation with the scalpriform incisors of the 

 Rodent ; thirdly, the fourth lobe of the right lung within 

 its own pleural cavity, in relation with which is the phrenic 

 nerve; and, lastly, the lobules of fatty tissue, already 

 spoken of, in apposition with the fourth and fifth of the 

 six sternal bones. 



q. Left azygos vein joining the vena cava superior of the same 

 side, and receiving some veins from the masses of fat just 

 mentioned in connection with the pericardium. 



r. Root of left lung : the lung of this side has been re- 

 moved; it consisted of a single lobe, as is often, though 

 not always, the ease in Rodentia, Marsupialia, and Insecti- 

 vora, though very rarely in Carnivora and Quadrumaua; 

 see Cuvier, Le9ons d' Anatomic Comparee, tom. vii. ed. sec, 

 1840, pp. 156-163. 



s. Kidney ; lying in the angle between the diaphragm and the 

 psoas and quadratus lumborum muscles. The smoothness 

 of its external surface is a mammalian character. 



t. Spleen. 



n. Stomach. 



