I.] DISSECTION OF A EABBIT AND OF A DOG. 17 



membrane, the visceral portion of the pleura, 

 maj be torn ; note that at the base of the lungs 

 this is continuous with the parietal portion of 

 the pleura attached to the walls of the chest 

 and bounding the mediastinum. Note the 

 position of the heart. 



13. In the mediastinum attached to the pleura note 

 on either side the phrenic nerve distributed to 

 the muscular fibres of the diaphragm. 



14. With fine forceps tear off the membrane over 

 the phrenic nerve in the middle part of its 

 course; another membrane will be seen under- 

 neath, outside of which the phrenic runs, this is 

 the parietal layer of the pericardium ; cut it 

 through, the heart will be seen to lie in a bag 

 formed by it. Remove the middle and posterior 

 portions of the sternum. Trace the connection 

 of the parietal layer of the pericardium with the 

 covering of the heart and of the roots of the 

 great vessels. 



15. Turning in the dog the heart and lungs over to 

 the right, pull up the large aortic trunk, and 

 note the almost transparent thoracic duct, 

 lying alongside the CESophagus ; trace it up to 

 its termiaation into the venous system (at the 

 junction of the left jugular and left sub-clavian 

 vein, cp. § 20). With a little care the thoracic 

 duct may also be traced in the rabbit. 



16. Prolong the median skin incision to the chin and 

 reflect the skin as far as possible. Observe on 

 L. 2 



