538 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



the trachea. It divides opposite to the second intercostal space or third rib into 

 the brachiocephalic and left brachial arteries. 



The brachiocephalic artery (A. brachiocephahca) is directed forward and a 

 httle upward in the anterior mediastinum, beneath the trachea. Opposite the 

 first rib it gives off the bicarotid trunk and is continued as the right brachial artery. 

 The latter (A. subclavia dextra) turns downward and bends around the anterior 

 border of the first rib and the insertion of the scalenus muscle above the brachial 

 vein. Its course and branches beyond this point will be described with the vessels 

 of the thoracic limb. 



The left brachial artery (A. subclavia sinistra) is longer than the right one and 

 rises to a higher level. It forms an almost semicircular curve, the concavity being 



Fir.. 42.S. — Topor.RAHHY of Thoracic Cavity of Horse, Lkft Side, aftkr Rkmovat. of Left Lung. 

 The ninth, fifteenth, and eighteenth ribs are retained, n. Pericardium; h, thoracic aorta; c, brachio- 

 cephalic trurdi; d, d" , dor.'ial arter.v; rf', subco.stal artery; e, e' , superior or deep cervical artery; /, vertebral artery; 

 (], a', left brachial arterj-; /(, inferior cervical artery; i, internal thoracic artery; k, common carotid artery; I, 

 jugular vein; ?n, brachial vein; ot', inferior cervical vein; n, anterior vena cava; o, thoracic duct; ;>, (rsophagus; 

 q, costal part of diaphragm; </, tendinous center of same; q" , left crus of same; r, anterior mediastinal l.vinph- 

 glands; s, trachea; t, bronchial lymph-glands; ii, root of left lung; r, anterior mediastinum; v' , posterior medi- 

 astinum; w, longus colli; r, sterno-cephalicus; ,//, scalenus; z, transversalis costarum; /, longissimus; 2, splenius; 3, 

 spinalis et semisi)inali.s; 4. 4' , rhomboideus; 5, left phrenic nerve; 6, left vagus; 6' , 6", oesophageal continuations 

 of vagi; 7, dorsal branch of right vagus; .?, cardiac nerve; 9, left recurrent nerve; /O, cervical trunk of s.vmpathetic; 

 //, first thoracic ganglion of sympathetic; 12, thoracic trunk of s.\nii)athetic; 13, brachial plexus. (.Vfter I'"!len- 

 berger-Baum, Toj). Anat. d. Pferdes.) 



ventral. It is related internally to the oesophagus, trachea, and thoracic duct, 

 and the left vagus, phrenic, and cardiac nerves cross under its origin. It emerges 

 from the thorax like the artery of the right side. There is thus a difference at first 

 between the trunks of opposite sides, but beyond this their course and distribution 

 are similar. 



The brachial and ])rachiocephalic arteries within the thorax give off the dorsal, 

 superior cervical, vertebral, and internal thoracic arteries. At the first rib they 

 give off the external thoracic and inferior cervical arteries. 



1. The left dorsal or dorso-intercostal artery (A. costo-cervicalis) passes 

 dorsally across the left face of the trachea and oesophagus toward the second 

 intercostal space. The right artery arises usually by a common trunk with the 



