MAMMALIA. 187 



5. Branches from the first thoracic ganglion, which communicate with others 



from the prolongation, and with a branch of the par vagum forming the 

 anterior pulmonary plexus, and then pass behind both auricles, to which they 

 are distributed. 



6. Right thoracic plexus: it arises from the third, fourth, and fifth thoracic 



ganglia ; below the root of the lung it communicates with a nerve 8, formed 

 from branches of each trunk of the par vagum, which gives branches to 

 the lungs ; it sends some branches behind the inferior vena cava, to give 

 branches to the left auricle and ventricle, and others to communicate with 

 the left thoracic plexus, accompanying the left azygos vein some way in 

 their course towards their termination in the left auricle and ventricle ; some 

 of its branches also pass behind the oesophagus to communicate again with 

 the left thoracic plexus. 



7. Prolongation appearing flat like tape, and composed of longitudinal threads 



communicating with each other, and having a slight difference in the form 

 of a ganglion at each spot where branches are given off to the aorta and 

 each intercostal nerve ; after the thoracic plexus is given off, it becomes 

 much narrower: it then gradually gets broader after every communication 

 with a spinal nerve, almost as if the branch from each intercostal nerve had 

 been added to it, and as if the splanchnic nerve were joined to it, as it would 

 be in man, if the prolongation and branches forming the splanchnic nerve 

 were drawn together; it is then continued through the diaphragm into the 

 semilunar ganglion, and forms a close connexion with the renal capsule, but 

 just about its termination in this it sends down the prolongation to the 

 lumbar ganglia, which send branches to the abdominal viscera, and com- 

 municate with the lumbar and sacral nerves. The branches from the 

 semilunar ganglion are very much like those in man, but not quite so 

 complex. 



8. Smaller or anterior branch of the trunk of the par vagum : it is joined by a 



branch from the left side, to form a small cord ; it communicates with the 

 thoracic plexuses, and gives branches to the lungs ; it passes anteriorly on 

 the oesophagus, then penetrates the diaphragm and receives a branch from 



B B 2 



