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 cesophagus, 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 
Fic. 553.—Topocraruy oF THORAX oF Horse, Lerr Sivek, AFTER REMOVAL OF LUNG, PERICARDIUM, AND GREATER 
Parr or MeprasTiInaL 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- 
a; 17, thoracic duct; 18, left 
vagus; 18’, wsophageal continuations of vagi; 19, left recurrent nerve; 20, left phrenic nerve (part which crosses peri- 
, sympathetic trunk; 23, great splanchnic nerve; 24, cesophagus; 
tercostal artery; 14, bicarotid trunk; 15, common carotid arteries; 16, anterior vena ces 
cardium indicated by dotted line); 21, cardiac nervy 
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 colli; 34, levator costs; 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 asophagus 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 
esophagus. 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 
‘In some cases the artery is too low to touch the cesophagus. 
