328 ANATOMY OF THE RABBIT 



the fourth cervical spinal nerve. That of the left side 

 crosses the ventral surface of the subclavian artery but 

 dorsal to the subclavian vein, then, lying just lateral to the 

 superior vena cava, crosses ventral to the aortic arch and 

 passes along the pericardium to the diaphragm (Fig. 112). 

 That of the right side passes back along the dorsolateral wall 

 of the superior caval vein, then along the pericardium, and 

 accompanies the thoracic portion of the inferior caval vein. 

 The phrenic nerves control the respiratory movements of the 

 diaphragm, each turning laterad when it reaches that organ 

 and being distributed in the muscular portions thereof on its 

 own side. 

 (/) The sympathetic trunk. At the base of the neck the cervical 

 portion of the sympathetic trunk enters the inferior cervical 

 ganglion (g. cervicale inferius). The latter lies in front of, 

 and somewhat dorsal to, the subclavian artery. The first 

 thoracic ganglion lies behind the artery and is connected 

 with the inferior cervical by the ansa subclavia, a loop 

 formed by two cords, one of which passes to the dorsal, the 

 other to the ventral side of the subclavian artery. 



The nerves proceeding from the inferior cervical gang- 

 lion enter the cardiac plexus and the sympathetic plexuses 

 of the subclavian and its branches. 



If desired, a useful view of the relations of the nervous 

 structures may be obtained before proceeding to the next 

 section by cutting away the left lateral wall of the thorax 

 and examining from that side the parts described in section 

 5 (pp. 335-337). 



3. Dissection of the heart. 



The character and relations of the sac enclosing the heart, the 

 pericardium, should first be noted. The relation to the heart of the 

 pericardium proper, or serous pericardium, is similar to that of the 

 peritoneum and pleura to the visceral organs which they invest 

 (p. 135). The serous pericardium comprises a parietal layer, which 

 lines the inner surface of a strong loose sac commonly known as the 

 pericardium, and a visceral layer, or epicardium, which forms an 

 intimately attached investment over the outer surface of the heart 



