THE NERVOUS SYSTEM. 227 



ventral half of the thoracic and abdominal walls should 

 be removed. By pushing the heart and lungs to the 

 left side a white cord about one millimeter in diameter 

 may be seen lying near the median dorsal line (Fig. 103). 

 The left cord may be found in a similar manner and 

 both followed cephalad and caudad, noting their numer- 

 ous branches in accordance with the following descrip- 

 tion. 



The sympathetic nerve=cord begins in the superior cervi- 

 cal ganglion lying near the angle of the mandible, beneath 

 the submaxillary and lymphatic glands. This ganglion 

 is about the shape of a grain of wheat, but not more 

 than half so large, and is adjacent to the small vagus 

 ganglion on the dorsal side of the carotid artery. The 

 ganglia are masses of large nerve cells and occur at regular 

 intervals on the sympathetic cords in the body cavity, 

 and are present also on some of the branches of the 

 cords (Fig. 104). On the cords there are three pairs 

 of cervical ganglia, thirteen pairs of thoracic ganglia, 

 seven pairs of lumbar ganglia, and one or two pairs of 

 sacral ganglia, in addition to two median unpaired 

 sacral ganglia. 



In the cervical region the sympathetic and pneumo- 

 gastric, or tenth cranial nerve, are bound in a common 

 sheath lying along the lateral aspect of the carotid 

 artery. One or two centimeters cephalad of the first 

 rib is the thyroid or middle cervical ganglion, whence the 

 nerve proceeds in two cords, enclosing the subclavian 

 artery, to the large inferior cervical ganglion just caudad 

 of the first rib. From the cervical portions of the sym- 

 pathetic cord are given off numerous delicate branches, 

 forming the carotid plexus on the carotid artery, and 

 uniting with the eight posterior cranial nerves and the 

 first spinal nerve. From the inferior cervical ganglion 



