COMMON BRACHIOCEPHALIC TRUNK OR ANTERIOR AORTA 



539 



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

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

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

 subcostal artery (A. intercostalis suprema) is the smaller. It passes backward 

 under the cost o- vertebral joints with the sympathetic trunk. It gives off the 

 second, third, and fourth intercostal arteries, and ends at the fifth space, where it 

 anastomoses with the first aortic intercostal artery, or constitutes the fifth inter- 

 costal artery, or dips into the longissimus muscle. It also gives off spinal branches 

 and twigs to the longus colli and the pleura. The other branch (A. transversa 

 colli) is the direct continuation of the trunk. It emerges through the upper end of 



Fig. 429. — Topography of Thoracic Cavity of IIdrse, Right View. 

 The ninth, fifteenth, and eighteenth ribs are retained, a. Pericardium; 6, posterior vena cava; e, vena 

 azygos; c', oesophageal vein; d, e, anterior vena cava; /, brachial vein; g, inferior cervical vein; h, jugular vein; 

 J, vertebral vein; k, superior cervical vein; I, dorsal vein; m, trachea; n, root of right lung; o, oesophagus; p, 

 mediastinal lobe of right lung; q, mediastinum; r, bronchial lymph glands; s, mediastinal lymph glands; t, costal 

 part of tliaiihragm; t' , tendinous center of same; u, intercostal muscle; r, longus colli; w, posterior deep pectoral 

 muscle; w' , anterior deep pectoral muscle; x, superficial pectoral muscle; y, sterno-cephalicus; z, scalenus; 1, 5, 

 right brachial artery; 2, dorso-cervical trunk; 2'. superior or deep cerxacal artery; S, dorsal artery (cut); 3', 

 subcostal artery; 4, internal thoracic artery; 6, external thoracic artery; 7, inferior cervical artery; 8, bicarotid 

 trunk; 10, aorta; 11, oesophageal artery; 12, thoracic duct; IS, right phrenic nerve; 14. brachial plexus; 15, 

 right vagus; 15', 15", oesophageal continuations of vagi; 16, right recurrent nerve; 17, cervical trunk of sympa- 

 thetic; IS. thoracic trunk of sympathetic; 20, inferior cervical ganglion; 21, first thoracic ganglion of sympathetic; 

 22, right cardiac nerve; 23, longissimus; 24, transversalis costarum; 25, spinalis; 26, multifidus; 27, ligamentum 

 nuchte. (After EUenberger-Baum, Top. .\nat. d. Pferdes.) 



the second intercostal space, passes across the transversalis costarum and longissi- 

 mus toward the withers, and divides into several diverging branches. An anterior 

 branch passes upward and forward between the splenius and complexus and anas- 

 tomoses with branches of the superior cervical artery; the others are directed 

 upward under the serratus magnus and rhoml^oideus to the withers, supplying 

 the muscles and skin of this region. 



The left dorsal artery sometimes arises with the superior cervical by a common trunk. On 

 the right side there may be a common stem for the dorsal, superior cervical, and vertebral ar- 

 teries. Occasionally the artery arises from the anterior aorta. Sometimes it emerges through 

 the third space. The subcostal may arise independently behind the dorsal or from the superior 

 cervical artery. 



