422 SPLANCHNOLOGY, OR ANATOMY OF THE VISCERA 



common carotid arteries and part of the thyroid gland. Between 

 it and the trachea ascend the recurrent laryngeal nerves. 



IN THE CHEST it is in relation, in front, with the trachea, 

 left bronchus, arch of the aorta and left carotid artery, and 

 pericardium; behind, with the spine, longus colli, thoracic duct, 

 and a portion of the descending thoracic aorta, where the 

 esophagus crosses from right to left before piercing the dia- 

 phragm; laterally, with the pleurae, and on the right side the 

 large azygos vein, and on the left the aorta except near the 

 diaphragm, where the aorta lies to the right side. The right 

 vagus is behind and the left in front of the esophagus, but at 

 first each is on the corresponding side. 



The arteries are derived from the inferior thyroid, a branch 

 of the thyroid axis of the subclavian; from the esophageal 

 and bronchial arteries, branches of the descending thoracic 

 aorta; the gastric from the celiac axis, and the left inferior 

 phrenic of the abdominal aorta. The veins form a plexus 

 on the outer side of the esophagus, emptying into the thyroid, 

 vena azygos major, and the gastric vein. Thus the portal 

 vein can communicate with the systemic veins. The lymphatics 

 drain into the inferior left cervical nodes, and the nodes of 

 the posterior mediastium. The nerves are derived from the 

 vagus and sympathetic system. They form the anterior and 

 posterior esophageal plexuses. 



THE PERITONEUM 



The peritoneum is a closed serous sac, which invests more 

 or less completely the contents of the abdominal and pelvic 

 cavities, sending in processes or diverticula between the adjacent 

 viscera. These processes are attached to the surfaces of the 

 viscera, forming their investment, and serving also to separate 

 and allow a free movement between them without friction. 

 Moreover, they confine the viscera to their proper relative 

 positions. 



The peritoneum is very thin, the attached surface being- 

 rough, the free, smooth and moist, and covered with a layer 

 of mesothelium. That part which is attached' to the inner 

 surface of the abdominal walls is called the parietal layer, 

 while that investing the viscera constitutes the visceral layer. 



