NEUROLOGY 275 



nerves, and from the same ganglion as the abducens ' and the motor 

 OCuH. It leaves the medulla oblongata from its ventral surface, and 

 passes with a posterior and an anterior branch out of the cranial 

 cavity through two separate foramina in the oS occipitale laterale. 

 The posterior branch, much smaller than the anterior, passes between 

 the cranial bones and the cervical sympathetic nerve; it then passes 

 at right angles through the rectus capitis anticus, and, while closely 

 following the "carotid artery, it fuses with the anterior branch; 

 The larger, anterior branch, much stronger than the posterior, sends 

 a short strong branch to the complexus muscle. The rest of this 

 branch, which probably has sjTnpathetic^ elements, is disposed as is 

 a spinal nerve. It crosses the sympathetic nerve, and at this point 

 forms a typical cervical sympathetic gangUon, It also forms a 

 short loop with the recurrent ventralis of the first cervical plexus. 

 From this loop, after it has given off several branches to the 

 muscles of the neck, it gives off one or two strong branches, which 

 fuse with each other and with the posterior thin branch, thus form- 

 ing the trunk of the hypoglossus. It receives many elements from 

 the first cervical nerves. ; 



The hypoglossus sometimes communicates with the vagus, crosses 

 over the latter, and divides itself into two main branches, as follows-} 



First, the recurrent laryngo-lingualis , which passes between the 

 cornua of the os hyoideum and the hsyax to the anterior part, 

 and furnishes the principal tongue muscles. It extends along the 

 inferior fUrf ace of the tongue and fuses with the one of the other 

 side and extends to the free tip of the tongue. This nerve probably 

 receives sensory elements from the second root and from the con- 

 fluent of the first cervical nerve. This form of anastomosis is well 

 marked in birds with thick tongues, as ducks. 



Second, the recurrent laryngeus furnishes the muscles of the su-, 

 perior larynx and of the tongue skeleton. It extends downward 

 and also furnishes the muscles of the trachea. It follows the course 

 of the jugular' vein and at the entrance of the chest suppUes the fur- 

 cula. The nerve passes into the thorax, downward along the side of 

 the bronchial tubes, and supplies innervation to all the muscles of 

 the inferior larynx. 



THE SPINAL CORD 



Structure of the Cord. — The spinal cord is called the myelon or 

 medulla spinaUs. It is a comparatively large, white, irregularly 



