202 Mammalia, 



jugular and subclavian veins, and forming the right subclavian 

 artery. Now the Student will see the reason of his care, for 

 crossing the subclavian artery at its point of origin, and run- 

 ning forwards parallel with the Trachea, at first external to the 

 carotid, and then crossing it about a quarter of an inch further 

 forwards than the bifurcation, is the right Pneumo- gastric 

 Nerve. This Nerve may now be traced back between the 

 Innominate Artery and the right cava, and forwards in com- 

 pany with the carotid artery. "We have thus demonstrated 

 on the right side, the Phrenic nerve on the right of tl\e right 

 cava, and the Pneumo -gastric on the left of the right cava, 

 at the point just opposite the cut end of the second rib. 



Now let the Student cut through the vena cava as it courses 

 round the^rs^ rib, and immediately dorsad of this vessel he will 

 find the Phrenic nerve continuing its straight course, and pass- 

 ing ventrad of the subclavian artery, about one eighth of an inch 

 from the spot where the Pneumo- gastric crosses it. This nerve 

 may be now followed up in the neck, and by this means its whole 

 course is exposed, which, briefly summarized, is as follows : 

 commencing in the cervical region near the Thyroid cartilage, 

 it courses down the neck, crosses the subclavian artery dorsad 

 of the vena cava superior, on the side of which it continues 

 to the Heart ; it then crosses ventrad of the roots of the 

 right Lung, and follows the course of the inferior cava to the 

 Diaphragm. 



If now the left vena cava descendens be slightly raised at 

 the corresponding point, the Student may, by careful dissection, 

 make out the difierence between the arrangement of arterial 

 branches on this side, as compared with the other. First 

 he will come upon, near the middle line, the left common 

 carotid artery, arising direct from the Aortic arch, across 

 which, closely adhering to the inner side of the left cava, he 

 will find the left Pneumo -gastric nerve to run ; and secondly, 

 a little deeper, he will come upon the left subclavian artery, also 



