File:Congdon1922-18-25.jpg

Figs. 18 to 25. The descent of the fourth aortic arch and the definitive aortic arch into the thorax

Shown in relation to the cervical vertebrae and ribs.

Legend

• Asterisk - so-called fifth aortic arch
• 4 - fourth aortic arch
• d. a. - definitive aortic arch
• R. 1 - first rib
• in. art. - innominate artery
• c. r. - cervical rib
• c. c - common carotid
• v. art. - vertebral artery
• a. r. - remnant of segment of dorsal aorta, interrupted between third and fourth aortic arches
• sub. art. - subclavian artery

In figures 20 and 24 the sternal bands are not yet in contact above and the definitive aortic arch has a large radius of curvature.

In figures 21 and 25 the bands have met and the arch has become sharply bent by the swinging dorsally of the heart.

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