744 CIRCULATORY SYSTEM OF THE DOG 
ally six pulmonary veins open into the left atrium. The bicuspid valve consists of two large cusps 
and four or five small ones. There are two musculi papillares in the left ventricle, both of which 
arise from the lateral wall; they are much larger than those of the right ventricle. 
THE ARTERIES 
The two coronary arteries usually spring separately from the origin of the aorta, 
but may arise by a common trunk. Each divides into circumflex and descending 
branches. The left artery is twice as large as the right one; it commonly gives off 
a branch of considerable size which runs in the intermediate groove. 
Fic, 613.—Vessets, Nerves, Erc., or THorax or Do; Ricut View. 
1, First rib (stump); 2, sternum; 2’, manubrium sterni; 2’’, xiphoid cartilage; 3, trachea; 4, esophagus; 6-8, 
ventral branches of fifth to eighth cervical nerves; 9, ventral branch of first thoracic nerve; 10, 10’, muscular and ten- 
dinous parts of diaphragm; 11, 11’, left ventricle and atrium of heart; 12, 12’, right ventricle and auricle of heart; 13, 
coronary groove; 14, night coronary artery; 15, middle cardiac vein; 16, pulmonary veins; 17, aorta; 18, thoracic 
duct; 19, anterior vena cava; 20, posterior vena cava; 21, dorsal intercostal vessels; 22, intercostal nerve; 23, inferior 
cervical (or omo-cervical) artery; 24, external thoracic artery; 25, brachial vessels; 26, common jugular vein; 27, in- 
ternal thoracic vessels; 28, sternal branches of internal thoracic vessels; 29, mediastinal arteries; 30, musculo-phrenic 
artery; 3/, anterior abdominal artery; 32, m. longus colli; 33, anterior mediastinal lymph glands; 34, sternal lymph 
glands; a, a’, right brachial artery and vein; 6, common carotid artery; c, deep cervical vessels; d, vertebral vessels; 
e, dorsal vessels; f, subcostal vessels; g, h, dorso-cervical trunks; 7, vena azygos; k, recurrent nerve; /, vago-sympathetic 
nerve; l’, l’, dorsal and ventral branches of vagus; m, phrenic nerve; n, roots of phrenic nerve; 0, thoracic trunk of 
sympathetic; 0’, nerve loop formed around brachial artery by branches which connect posterior cervical and first tho- 
racic ganglia of sympathetic (Ansa subclavia); p, thoracic ganglia of sympathetic; g, rami communicantes; r, posterior 
cervical ganglion; s, first thoracic ganglion; ¢, uw, », rami communicantes between s and seventh cervical, first thoracic, 
and eighth cervical nerves; w, cardiac branch of first thoracic ganglion; x, cardiac branches of posterior cervical gan- 
glion; y, bronchial branches of vagus; z, depressor nerve. (After Bucher.) 
The aorta runs at first almost straight forward and then turns backward, 
forming a very sharply curved arch. It gives off at its origin the two coronary 
arteries. From the convexity of the arch two large vessels arise. The first and 
larger of these is the brachiocephalic artery; this runs forward at first on the 
ventral surface of the cesophagus, then under the trachea. It gives off in succession 
the left and right common carotid arteries, and turns around the first rib as the 
right brachial artery. The left brachial artery passes forward on the left face of 
the cesophagus, forming a slight arch (concave ventrally), and turns around the first 
rib. The intrathoracic branches of the brachial arteries are as follows: 
