210 PRACTICAL ANATOMY. 



7. The intercostal nerves, each giving off" two communicating branches ranii 

 coinnmnicantes to the ganglia of the sympathetic nerve in the thorax. 



Dissection of these regions must be done with the forceps. No cutting instru- 

 ment should be used. Proceed in this order: (i) Find the phrenic nerve, a 

 branch of the third and fourth cervical, and the arteria comes nervi phrenici, a 

 branch of the internal, mammary artery, on either side of the pericardium, 

 between this structure and the pleura. This nerve comes from the third and fourth 

 cervical plexus. It lies on the scalenus anticus muscle in the neck. It enters 

 the mediastinal space between the subclavian artery and vein. It passes anterior 

 to the root of the lung. It communicates with the sympathetic, with the nerve 



SUP* v. c 



FORAMEN OVALE 



PLAC E N T A 

 Fu;. 148. SCIIKMU OK THE ]''<KTAI. CIRCULATION. 



to the subclavius, and with the ansa hypoglossal loop. It is distributed to the 

 diaphragm, pleura, pericardium, and diaphragmatic peritoneum. 



The pericardium has : (i) A base, attached to the diaphragm ; (2) an apex. 

 continuous above with the third layer of deep cervical fascia. It may have 

 much fat. It has a visceral layer, a parietal layer, and a cavity. The latter is 

 the space between the two layers, and contains a small quantity of fluid for lubri- 

 cation. It may contain many ounces of fluid this is hydro-pericardium. Note 

 the relation of the inflated lung to the pericardium and poststernal connective 

 tissue. (Fig. I IO.) Make traction on the diaphragm where the pericardium is 

 attached, and observe that this cannot IK- depressed because of its continuity with 

 the third layer of the cervical fascia. Inflate the pericardiac sac ; then cut the 

 parietal layer of the pericardium. 



