204 Mammalia, 



noted in contradistinction to the direction of the Aortic arch 

 in the Bird. 



By turning up the apex of the Heart, the course of 

 the left vena cava may be traced round the base of the 

 ventricles behind, dorsad of the pulmonary vessels (which 

 may be seen on either side towards the Lungs), to be joined 

 some distance to the left of the right auricle by the ascend- 

 ing cava, forming a large sinus at the back of the Heart. 



Examination of Trachea. The Student should now 

 cut across the right vena cava descendens near the auricle, 

 and the Aorta near the Heart, and pressing the Heart 

 backwards dissect awav the connective tissue and remains 

 of pericardium at its base. By this means he will be 

 enabled to see the bifurcation of the pulmonary artery, 

 and just internal to this, but following the same direc- 

 tions, the subdivision of the Trachea into the two Bronchi : 

 the swelling contained within the angle of the pulmonary 

 artery being the point of junction of all the pulmonary veins 

 on their entrance into the left auricle. By cutting through 

 these Pulmonary vessels as they come into view, and lastly by 

 cutting through the ascending cava near its entrance into the 

 right auricle, the Heart may be removed. 



The Heart differs little from that of the Sheep, and it will 

 therefore be unnecessary to enter here into a particular in- 

 vestigation. The enormous thickness of the walls of the left 

 ventricle, and the extreme tenuity of the walls of the right 

 ventricle should, however, be noted, as also the great extent 

 of the sinus at the back. 



Removal of Right Lung. The Trachea may be now 

 cut through just posterior to the arch of the Aorta; but 

 care must be taken not to cut through, at the same time, 

 the (Esophagus, which is closely adherent to the dorsal 

 aspect of the Trachea at this point : and the right Lung 

 removed. Here the Student should remark that the 



