632 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



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 

 ventral. It is related medially 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 



Fig. .553. — Topography of Thorax of Hohse, Left Side, after Removal of Lukg, Pehicahdium, and Greater 



Part of Mediastinal Pleura. 

 1, Right ventricle; 1', left ventricle; 2, right auricle; 2', left auricle; 3, pulmonary artery; 3', left branch of 3; 

 4, aorta; -5, brachiocephalic trunk; 6, left brachial vessels; 7, dorsal artery; 7', subcostal artery; 8, deep cervical 

 artery; 9, vertebral artery; 10, internal thoracic artery; 11, musculo-phrenic artery; 12, inferior cervical artery; 13, in- 

 tercostal artery; 14, bicarotid trunk; 1.5, common carotid arteries; 16, anterior vena cava; 17, thoracic duct; IS, left 

 vagus; 18', CESophageal continuations of vagi; 19, left recurrent nerve; 20, left phrenic nerve (part which crosses peri- 

 cardium indicated by dotted line) ; 21, cardiac nerve; 22, sympathetic trunk; 23, great splanchnic nerve; 24, oesophagus; 

 25, trachea: 26, left bronchus; 27, pulmonary veins; 28, apical lobe of right lung; 29, basal border of left lung indicated 

 by dotted line; 30, diaphragm; 30', diaphragmatic line of pleural reflection; 31, 32, external and internal intercostal 

 muscles; 33, longus colh; 34, levator costfe; 35, multifidus dorsi. 



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

 are similar. 



The left brachial and brachiocephalic arteries give off within the thorax the 

 dorsal, deep cervical, vertebral, and internal thoracic arteries. At the first rib each 

 gives off the external thoracic and inferior cervical arteries. 



1. The dorsal or costo-cervical artery (A. costo-cervicalis) of the left side 

 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 

 deep cervical, crosses the right face of the trachea, and has no contact with the 

 oesophagus. Both detach small branches to the trachea, mediastinal lymph glands, 

 and pleura, and on reaching the longus colli divide into two branches. Of these, the 



1 In some cases the artery is too low to touch the oesophagus. 



