792 THE VASCULAR SYSTEM. ' 
Deep Palmar Arch (arcus volaris profundus, Fig. 564).—The deep palmar 
arch extends from the base of the metacarpal bone of the little finger to the upper 
end of the first interosseous space, and is formed by the terminal part of the radial 
artery, anastomosing with the deep branch of the ulnar. It is from half to three 
quarters of an inch (12 to 18 mm.) above the level of the superficial palmar arch, and 
it lies deeply in the palm, in contact with the bases of the metacarpal bones and 
ligaments and on the origin of the interossei muscles; it is under cover of the flexor 
tendons and their synovial sheaths. 
Branches.—(a) The superior perforating (rami perforantes); three small arteries 
which pass backwards through the inner three interosseous spaces, and between the origins 
of the dorsal interossei muscles. ‘They anastomose on the dorsum of the hand with the 
dorsal interosseous arteries. 
(6) Small irregular recurrent branches pass upwards and unite with the anterior 
carpal arch. 
(c) The articular to the adjacent articulations. 
(7) The palmar interosseous arteries (aa. metacarpez volares) are three vessels which 
pass downwards on the interosseous muscles of the three inner spaces and under cover of 
the flexor tendons. They terminate by anastomosing with the palmar digital arteries just 
before the latter vessels divide into collateral branches. 
(ce) The communicating, a small irregular branch which passes inwards between the 
flexor tendons and the short muscles of the little finger to anastomose with the innermost 
palmar digital artery. 
BRANCHES OF THE DESCENDING THORACIC AORTA. 
The branches given off from the thoracic portion of the descending aorta are 
distributed chiefly to the walls of the thorax and to the thoracic viscera. They 
contribute also to the supply of the spinal cord and its membranes, and to that 
of the vertebral column and of the upper part of the abdominal wall. The 
branches, which are numerous and for the most part arranged in pairs, are as 
follows :— 
Intercostal. Bronchial. 
: Subcostal. ; (Esophageal. 
Parietal.< 7. ; Visceral. m see 
Diaphragmatic. Pericardial. 
The vas aberrans. Mediastinal. 
PARIETAL BRANCHES OF THE DESCENDING THORACIC AORTA. 
1. Intercostal Arteries (a. intercostales).— There are nine pairs of aortic 
intercostal arteries. They usually arise separately, though not uncommonly a 
pair may take origin by a common trunk from the back of the aorta, and are 
distributed to the lower nine intercostal spaces, to the spinal column, to the 
contents of the spinal canal, and to the muscles and skin of the back. The 
third, fourth, and fifth on each side also give branches to the mammary gland. 
The arteries of opposite sides closely correspond, but, since the aorta in the 
thoracic region lies on the left side of the spinal column, the right intercostal 
arteries cross the front of the vertebral column, behind the cesophagus, the thoracic 
duct, and the vena azygos major, and are longer than the left arteries. In other 
respects the course of ‘all the aortic intercostal arteries is almost identical. They 
run outwards and backwards on the sides of the bodies of the vertebree to the inter- 
costal spaces, passing behind the pleura, and being crossed, opposite, the heads of 
the ribs, by the sympathetic cord. The lower arteries are also crossed by the 
splanchnic nerves, and those on the left side are in addition crossed by the smaller 
azygos veins. On reaching an intercostal space each artery runs upwards, some- 
times behind, sometimes in front of the corresponding intercostal nerve, to the 
upper border of the space, along which it is continued in the subcostal groove. It 
lies at first between the pleura and the posterior intercostal membrane, immediately 
below the intercostal nerve; it then pierces the intercostal membrane, and runs 
between it and the external intercostal muscle as far as the angle of the rib, 
beyond which it is continued forward between the internal and external intercostal 
