circulation through the intercostal arteries that results from a circulatory
deficit elsewhere. Just as a subcostal location offers protection to the inter-
costal neurovascular bundle, fracture of a rib may involve tearing of these
structures. The intercostal neurovascular bundle components give off a
smaller accessory bundle, which lies adjacent to the upper border of the
ribs. Thoracocentesis usually is performed adjacent to the upper border of
the ribs (answer a)to avoid the main intercostal neurovascular bundle.
Deep to the posterior intercostal membrane (answer d)isnotanatomically
relevant.
346.The answer is d.(Sadler, pp 180–183. Moore and Persaud, Develop-
ing, pp 361–365.)Branches of the arteries of the sixth aortic arches form
the pulmonary arteries. In addition, the left sixth arch artery forms the
ductus arteriosus. The blood supply to the right side of the heart
(answer a)is primarily derived from the right and left coronary arteries
derived from the truncus arteriosus. The face (answer b)and thyroid
gland(answer c)receive blood primarily from the facial and superior
thyroid arteries, respectively. These are branches of the common and
external carotid arteries which, in turn, are derivatives of the second and
third aortic arch arteries. The upper digestive tract (answer e)is supplied
by the celiac and superior mesenteric arteries, derivatives of the vitelline
arteries.
347.The answer is c.(Moore and Dalley, pp 156–159.)The sinoatrial
artery arises from right coronary artery about 60% of the time and arises
from the left circumflex artery about 40% of the time, thus notalways from
either the right (answer a)or left (answer b)coronary artery. Coronary
occlusions involving the right coronary artery are, therefore, often accom-
panied by rhythm disturbances. The right marginal (answer d)isnot
involved in supplying blood to the sinoatrial node. While it is true that the
posterior interventricular artery (answer e)can receive blood mainly from
either the right or left coronary arteries (so called right or left “dominant”
patterns) the sinoatrial artery usually does notarise from this region.
348.The answer is c.(Moore and Dalley, pp 159–162.)With the excep-
tion of the anterior surface of the right ventricle, blood returning from the
coronary circulation collects in the coronary sinus, which, in turn, empties
directly into the right atrium. Both the superior (answer e)and inferior
Thorax Answers 483