118 THE ANATOMY OF THE HORSE. 



nerve. ^Yhen it is fully constituted the first right nerve creeps over the base of the 

 heart, turns round the root of the aorta, and mixes its terminal filaments with those of 

 the left cardiac nerves. The second right cardiac nerve is formed by the union of three 

 branches which take origin in sxiccession from the corresponding pneumogastric, behind 

 the dorsal artery, along the right side of the trachea. This nerve is in communication 

 with the sympathetic of the dorsal region by three branches which approach the last 

 beneath the first, fourth, and sixth ribs. 



When the second right nerve arrives above the termination of the anterior vena cava, 

 it divides into two branches : the one is tlrrown into the roof of the auricles ; the other, 

 reinforced by a filament coming from the pneumogastric, is expended, by numerous ^ 

 filaments, on the surface of the left ventricle ; some reaching as far as the right ventricle. 



The f oiu? secondary filaments are arranged like the steps of a ladder on the portion of 

 the pneumogastric comprised between the entrance of the chest and the division of the 

 bronchi. These filaments are expended in the great vessels and in the walls of the heart. " 

 — Chauveau. " Traits d'anatomie comj)arie des animaux domestiques,"] 



The Bight Dorsal Cord of the Sympathetic does not differ materially 

 from tlie left. 



The PosTBRiOE AoETA is here seen in a large part of its course, but it has 

 already been fully described in connection with the left side. It detaches 

 to this side thirteen intercostals, exactly similar to those of the left. 



The Beoncho-CEsophageal Arteet. This artery arises from the 

 convexity of the aortic arch, a little anterior to the bifurcation of the 

 trachea. Generally, as in Plate 24, it arises not independently but as 

 a division of a short vessel which is at the same time the comfnon 

 trunk for the 1st and 2nd pairs of aortic intercostals. It is a small 

 vessel, not larger than an intercostal. It is reflected downwards and 

 backwards on the right side of the aorta, and divides into the bronchial 

 trunk and the oesophageal artery. The (esophageal artery, which is the 

 smaller of the two, is continued backwards above the gullet, through the 

 posterior mediastinum, extending sometimes to near the foramen sinis- 

 trum, and anastomosing with the pleuro-cesophageal branch of the 

 gastric artery. Sometimes there is an analogous vessel in the mediasti- 

 num below the oesophagus (inferior oesophageal), but when present this is 

 a very slender artery. The bronchial trunk dips down between the 

 aorta and the gullet, and bifurcates to form the right and left bronchial 

 arteries, each of which enters the root of the lung on the bronchus. It 

 is the nutrient vessel to the lung. The above-mentioned inferior oesopha- 

 geal may be a branch of one of the bronchial arteries. 



The Aeteria Innominata is the right division of the anterior aorta, 

 the left axillary artery being the other division. In calibre it is greater 

 than the left axillary, and it is placed on a lower level. It is related to 

 the trachea above ; and to the anterior vena cava below and to the left. 

 After a course of about two inches, it divides to form the cephalic trunk 

 and the right axillary artery, and immediately in front of its point of 

 division it detaches the dorso-cervical artery. 



The Doeso-cervioal Arteey. This is a short trunk which passes 

 upwards on the trachea, and divides to form the dorsal and superior 



