794 THE VASCULAR SYSTEM. 
it represents the dorsal roots of the fourth and fifth right aortic arches of the 
embryo. When present it arises from the front and right ‘side of the upper part of 
the main trunk near the upper bronchial artery, and passes upwards and to the 
right behind the cesophagus; it frequently anastomoses with the right superior 
intercostal artery, and it may be enlarged and form the first part of the right 
subclavian artery. 
VISCERAL BRANCHES OF THE DESCENDING THORACIC AORTA. 
The bronchial branches (aa. bronchiales) of the thoracic aorte are usually two 
in number—an upper and a lower—and both pass to the left lung. The wpper left 
bronchial artery arises from the front of the main trunk opposite the bifurcation 
of the trachea; the ee left bronchial artery usually takes origin near the 
lower border of the left bronchus. Both vessels are directed downwards and out- — 
wards to the back of the bronchus, which they accompany, and, dividing similarly, 
they follow its ramifications in the lung. They not only supply the walls of the 
bronchial tubes and the substance of the lungs, but also give branches to the 
bronchial glands, the pulmonary vessels, the pericardium, and the cesophagus. 
Asa rule there is only one right bronchial artery, and it arises from the first — 
right aortic intercostal artery; but it not uncommonly arises from the upper left — 
bronchial artery, and more rarely it springs directly from the aorta. In its course — 
and distribution it corresponds to the bronchial arteries of the left side. : 
The cesophageal branches (aa. cesophagew) are variable; usually four or five 
small branches spring from the front of the aorta and pass forwards to the : 
cesophagus, in the walls of which they ramify, anastomosing above with branches 
of the left bronehial and inferior thyroid arteries, and below with cesophageal 
branches of the coronary and phrenic arteries. 
The pericardial branches (rami pericardiaci) consist of three or four small 
Pre ine vessels which are distributed on the surface of the pericardium. 
4. Small mediastinal branches (rami mediastinales) pass to the areolar tissue — 
and glands in the posterior mediastinal space, and to the posterior part of the — 
diaphragm. 
BRANCHES OF THE ABDOMINAL AORTA. 
The branches of the abdominal portion of the aorta are distributed almost 
entirely to the walls and contents of the abdominal cavity, but some also supply 
small branches to the vertebral column, and to the contents of the spinal canal, and 
others are prolonged into the pelvis. They are divisible into parietal and visceral 
groups, both of which include paired and single (unpaired) vessels. 
( Suprarenal, 
Inferior phrenic. Paired.) Renal. 
Paired., Lumbar Srsmmanie or ovarian, 
Common iliac. ‘Ceeliae axis. 
Single. Middle sacral. Single.- Superior mesenteric. 
| Inferior mesenteric. 
Parietal.- Visceral. - 
) 
. 
PARIETAL BRANCHES OF THE ABDOMINAL AORTA. 
1. The inferior phrenic arteries (aa. phrenic inferiores, Fig. 566) are two 
in number, and are of small size; they arise, either separately or by a common 
trunk, from the aorta immediately below the diaphragm, on the under surface 
of which they are distributed. Diverging from one another, each artery runs 
upwards and outwards on the corresponding crus of the diaphragm—that on the 
right side passing behind the inferior vena cava, that on the left behind the ceso- 
phagus—and just before reaching the central tendon of the diaphragm it divides 
into internal and external terminal branches, The internal branch of each artery 
runs forward and anastomoses with its fellow of the opposite side, forming an arch, 
convex forwards, along the front of the central tendon of the diaphragm. Offsets 
from this arch anastomose with the superior phrenic, musculo-phrenic, and internal 
