The =left subclavian= (Fig. 118, _c_) arises from the convexity of the
aortic arch just distad of the origin of the innominate artery, and
about two or three centimeters from the heart. It passes craniad and
slightly to the left, and turns into the left arm just craniad of the
first rib.
The =right subclavian= (Fig. 115, _n_) is a direct continuation of the
innominate, the artery receiving the name subclavian after the right
common carotid is given off, usually at about the level of the second or
third intercostal space.
The subclavian has the following branches: the =vertebral artery= (Fig.
118, _g′_), the =internal mammary= (Fig. 118, _h_), the =costocervical
axis= (Fig. 118, _g_), the =thyrocervical axis= (Fig. 118, _j_). Beyond
the last-named branch it continues into the arm as the =axillary= artery
(Fig. 118, _i_; Fig. 122, _g_).
[Illustration: FIG. 121.--ARTERIES OF THE VENTRAL SURFACE OF THE
BRAIN.
_a_, A. vertebralis; _b_, A. spinalis anterior; _c_, A. basilaris;
_d_, A. cerebelli inferior posterior; _e_, A. cerebelli anterior; _f_,
A. cerebri posterior; _g_, cut ends of the two internal carotid
arteries; _h_, cut ends of branches from the carotid plexus (_g_ and
_h_ are placed within the circulus arteriosus or circle of Willis);
_i_, A. cerebri media; _j_, A. cerebri anterior.]
_a._ =A. vertebralis= (Fig. 118, _g_′).--The vertebral artery arises
from the dorsal surface of the subclavian opposite the first rib. It
passes craniad and dorsad at the side of the thoracic portion of the
longus colli muscle, and enters the foramen transversarium of the sixth
cervical vertebra. It passes thence craniad through the foramina
transversaria (which together form the =vertebrarterial canal=) and
gives off at the intervertebral foramina branches to the muscles of the
neck and branches which pass across the ventral surface of the spinal
cord to join A. spinalis anterior. Craniad of the foramen transversarium
of the atlas the vertebral artery turns dorsad in the groove on the
lateral surface of the atlas. Here it gives off a large branch which
passes laterodorsad to the muscles of the neck and may anastomose with a
branch of the occipital artery. The vertebral artery then passes into
the vertebral canal through the atlantal foramen. It passes to the
ventral side of the spinal cord and unites at about the level of the
foramen magnum with the vertebral artery of the opposite side (Fig. 121,
_a_) to form the =basilar artery (A. basilaris)= (Fig. 121, _c_), which
passes craniad along the ventral middle line of the brain. Just before
their union the two vertebral arteries (_a_) give off each a branch
which passes caudomediad. These two branches soon unite in the middle
line, forming the =anterior spinal artery= (=A. spinalis anterior=)
(_b_), which passes caudad the entire length of the spinal cord, lying
on its ventral middle line and receiving many communicating branches
from the vertebral, intercostal, and lumbar arteries.
=A. basilaris= (_c_).--This arises by the union of the two vertebral
arteries in the manner just described. It passes craniad along the
ventral middle line of the medulla and pons, giving numerous small
branches to these structures. A large branch, =A. cerebelli inferior
posterior= (_d_), passes on each side to the caudal surface of the
cerebellum, on which it ramifies. At the cranial margin of the pons the
basilar artery divides. From each division a very large branch passes
on each side across the pedunculi cerebri to the cranial part of the
cerebellum; this is =A. cerebelli anterior= (_e_). Just craniad of this,
arising from nearly the same point, the smaller =A. cerebri posterior=
(_f_) passes laterad to the caudal part of the cerebrum; it is joined by
the internal carotid artery (_g_). The small continuations of the two
halves of =A. basilaris= then pass craniad at the side of the hypophysis
to join the posterior communicating branches from the carotid plexus. As
other branches of the carotid plexus unite across the middle line
craniad of the optic chiasma, an arterial circle is formed on the base
of the brain, surrounding the hypophysis and the optic chiasma. This is
known as the =circulus arteriosus=, or circle of Willis (see page 289).
_b._ =A. mammaria interna= (Fig. 118, _h_).--The internal mammary artery
rises from the ventral surface of the subclavian opposite the first rib,
and passes in the mediastinum ventrocaudad to reach the sternum opposite
the third intercostal space. It sends two or three small branches
craniad to the midventral part of the thoracic wall and then extends
caudad at the side of the sternum. It sends off lateral branches to the
ventral thoracic wall, branches to the mediastinum and pericardium, a
branch to the diaphragm which anastomoses with the phrenic; and finally
it passes out of the thoracic cavity caudad of the last costal
cartilage, extends caudad in a zigzag course at the lateral border of
the rectus muscle and anastomoses with the inferior epigastric artery.
_c._ =Truncus costocervicalis= (Fig. 118, _g_).--The costocervical axis
arises from the subclavian opposite the first rib, passes craniodorsad,
and divides almost at once into two branches. The smaller one of these,
the =superior intercostal= (=A. intercostalis suprema=), passes caudad
and, dividing, supplies the first and second intercostal spaces, and
then passes to the deep muscles of the back. The other branch divides
almost immediately into two. One of these, =A. transversa colli=, passes
laterad in front of the first rib and enters the serratus anterior
muscle. In this it passes dorsad, giving off branches to this muscle and
to the levator scapulæ, till it reaches M. rhomboideus, which it
likewise supplies. The other branch (=A. cervicalis profunda=), which
seems to form a continuation of the main artery, passes directly dorsad
and leaves the thoracic cavity between the heads of the first and second
ribs. Here it passes into the deep muscles of the neck; it can be traced
in the substance of the complexus muscle as far forward as the atlas.
_d._ =Truncus thyrocervicalis= (Fig. 118, _j_).--The thyrocervical axis
(or thyroid axis) arises from the subclavian beneath the first rib, a
short distance distad of the origin of the costocervical axis. It passes
laterocraniad and dorsad, lying on the mediocranial side of the brachial
plexus. A short distance from its origin it gives off a branch, varying
much in size, the =cervicalis ascendens= (Fig. 119, _d_), which passes
craniad on the ventral side of the neck, supplying the sternomastoid,
sternohyoid, the cervical portion of the scalenus, and sometimes other
muscles of the neck region. Other branches pass from the thyroid axis to
the inner surface of the clavotrapezius (Fig. 122, _a_) and to the
ventral end of the pectoral muscles. At the level of the cranial border
of the scapula the artery takes the name =A. transversa scapulæ=, or
=suprascapularis=. This divides into three main branches. The first
branch, sometimes large, sometimes small, passes to the lymphatic gland
in the hollow of the shoulder, and to the adjacent muscles; it supplies
the clavotrapezius, acromiotrapezius, levator scapulæ ventralis,
splenius, occipitoscapularis, and rhomboideus. A second branch passes
between the subscapularis and supraspinatus muscles, dividing into
various branches which supply the muscles named. The third branch
pierces the supraspinatus muscle, just craniad of the acromion process,
and ramifies in that muscle.
_e._ =A. axillaris= (Fig. 122, _g_).--The axillary artery is the
continuation of the subclavian laterad of the first rib. It lies caudad
of the brachial plexus and parallel to it. It sends off the following
branches:
1. =A. thoracica anterior= (Fig. 122, _h_).--The anterior thoracic is a
slender artery which leaves the ventral side of the axillary opposite
the first rib and passes caudomediad, to supply the medial ends of the
pectoral muscles (_g_).
2. =A. thoracica longa= (_p_).--The long thoracic artery is larger than
the preceding, leaves the axillary a short distance laterad of it, and
passes caudad to the middle portions of the pectoral muscles (8) and
continues to the inner surface of the latissimus dorsi.
A short distance beyond the long thoracic the axillary divides into two.
The more cranial one of these is the =subscapular= (_l_); the other is
the =brachial= (_g_′).
3. =A. subscapularis= (_l_).--The subscapular artery passes laterad and
gives off a short distance from its origin the =A. thoracicodorsalis=
(_t_) and =A. circumflexa humeri posterior= (see below); it may also
give rise to the =circumflexa anterior humeri= (_l_′), and to the
=profunda brachii= (_u_); these two branches, however, rise more
frequently from the brachial artery (_g_′) and are described in
connection with it. The subscapular artery then passes through the
triangular interval between the scapular end of the long head of the
triceps, the latissimus dorsi, and the glenoid border of the scapula.
Within this interval it sends muscular branches to the long head of the
triceps, the subscapularis, and the latissimus dorsi. That to the latter
muscle is very large. At the border of the scapula, opposite the
tuberosity of the spine, it turns craniad, passes over the lateral
surface of the infraspinatus muscle, supplying it; crosses the spine,
and sends branches into the supraspinatus fossa in both directions
parallel to the scapular spine. These supply the supraspinatus,
acromiotrapezius, and spinotrapezius, and anastomose with the branches
of the transversa scapulæ. As the subscapularis turns craniad onto the
surface of the infraspinatus it sends dorsad a small branch, the
=circumflexa scapulæ=, which passes in the infraspinatus fossa close to
its glenoid border as far as the glenovertebral angle, supplying the
infraspinatus and latissimus dorsi by lateral branches.
[Illustration: FIG. 122.--BLOOD-VESSELS AND THE MORE VENTRAL NERVES OF
THE AXILLA, VENTRAL VIEW.
The pectoral and clavobrachial muscles have been cut and laid aside,
their ends being shown; only a part of the nerves are exhibited. 1, M.
clavobrachialis; 2, cut end of M. pectoralis major; 3, cut end of M.
pectoralis minor; 4, M. biceps; 5, M. teres major; 6, M.
epitrochlearis, partly cut and turned back; 7, M. latissimus dorsi,
partly cut; 8, M. pectoralis minor; 9, M. pectoralis major; 10, short
portion of caput mediale of M. triceps brachii. _a_, branches of the
thyrocervical axis to clavobrachial and clavotrapezius muscles; _b_,
suprascapular nerve; _c_, first subscapular nerve; _d_,
musculocutaneous nerve; _e_, median nerve; _f_, V. axillaris; _f_′, V.
brachialis; _g_, A. axillaris; _g_′, A. brachialis; _h_, first
anterior thoracic nerve, accompanied by the anterior thoracic artery
and vein; _i_, V. subscapularis; _j_, large muscular branch (to
subscapular muscle) of the subscapular vein and brachial artery; _l_,
A. subscapularis; _l_′, A. circumflexa humeri anterior; _m_, radial
nerve; _n_, ulnar nerve; _o_, medial cutaneous nerve; _p_, A.
thoracica longa; _q_, _r_, second anterior thoracic nerve; _s_, V.
longa thoracica; _t_, A. and V. thoracicodorsalis; _u_, A. profunda
brachii; _v_, branch of brachial artery accompanying medial cutaneous
nerve; _w_, branch of A. collateralis radialis superior; _x_, A.
collateralis radialis superior; _y_, V. mediana cubiti; _z_, A.
collateralis ulnaris.]
=A. thoracicodorsalis= (_t_).--This arises from the subscapular a short
distance from its origin and passes across the teres major to the
latissimus dorsi (7), giving branches to both these muscles and to the
epitrochlearis.
=A. circumflexa humeri posterior.=--The posterior circumflex artery
arises from the A. subscapularis close to the origin of the latter. It
passes between the subscapularis muscle and the teres major, close to
the border of the biceps, then between the lateral and long heads of the
triceps. It gives off a branch to the inner surface of the spinodeltoid
and acromiodeltoid, then passes distad to supply the lateral and long
heads of the triceps.
4. =A. brachialis= (_g_′).--The brachial artery is the continuation of
the axillary (_g_) into the arm beyond the origin of the subscapular
(_l_). It passes along that side of the biceps which lies next to the
humerus. It passes thus, accompanied by the brachial vein (_f_′) and
median and ulnar nerves, through the bicipital arch and afterwards
between the biceps (4) and the intermediate division of the medial head
of the triceps to the supracondyloid foramen of the humerus, through
which it passes with the median nerve to reach the concavity of the
elbow. It gives off the following branches:
_a._ =A. circumflexa humeri anterior= (_l_′).--The anterior circumflex
artery usually leaves the brachial near its origin (but may arise from
the subscapular (_l_) or one of its branches); it passes to the biceps
(4) near the origin of the latter and sends a branch proximad to the
head of the humerus.
_b._ =A. profunda brachii= or superior profunda (_u_).--This arises from
the first part of the brachial or it may come off from one of the
branches of the axillary (e.g., the subscapularis). It passes along with
the radial nerve onto the dorsal side of the humerus and supplies the
triceps muscle. It also sends branches to the epitrochlearis (6) and
latissimus dorsi (7).
_c._ =Rami musculares.=--Muscular branches are given off near the
supracondyloid foramen to the biceps (4), epitrochlearis (6), and
brachialis muscles. A nutrient artery leaves the brachial proximad of
the supracondyloid foramen, either separately or in common with the
muscular branches, and passes into the nutrient foramen at the junction
of the middle and distal thirds of the shaft of the humerus, supplying
the bone.
_d._ =A. collateralis ulnaris= (superior) (or A. anastomotica magna)
(_z_).--This leaves the brachial artery just proximad of the
supracondyloid foramen and passes to the convexity of the elbow,
supplying the structures about the olecranon.
_e._ =A. collateralis radialis superior= (Fig. 130).--This rises from
the axillary artery just proximad of the supracondyloid foramen (Fig.
122, _x_), in company with the vena mediana cubiti (_y_), passes
across the surface of the biceps (4), beneath the pectoantibrachialis,
into the concavity of the elbow. Here it gives branches to the
pectoantibrachialis, clavobrachialis, and extensor muscles of the
forearm. It then passes onto the ventroradial border of the forearm
(Fig. 130) and runs along this border, in company with the vena
cephalica (Fig. 130, _c_) and the superficial radial nerve (_g_), to the
wrist, sending off branches to the integument. At the wrist it turns
onto the dorsum of the hand, passing in a gentle curve to the ulnar side
and distad, and giving off a branch for the space between each pair of
metacarpal bones. These branches (Fig. 130, _e_) (=Aa. digitales
dorsales=) pass distad and anastomose with branches coming from the
palm.
_f._ =A. radialis= (Fig. 123).--Distad of the convexity of the elbow the
brachial artery takes the name =radial artery=. It passes from the
supracondyloid foramen on the medial side of the biceps tendon (1) and
beneath the pronator teres muscle (5), giving off small branches, as far
as the middle of the forearm, where it gives off the ulnar artery (_k_).
It then passes from beneath the pronator teres (5) and lies on the
surface of the fifth part of the flexor profundus (8), covered only by
the fascia and integument. Near the wrist it sends off a branch (_m_)
toward the ulnar side of the arm, which passes into the palm on the
surface of the tendon of the flexor profundus, giving twigs to the
digits and to the pad in the palm. A branch from this may join the
ulnar, and the common trunk thus formed passes into the hand and gives
origin to the branches described under the ulnar artery. The presence
and size of this branch of the radial varies with the size of the ulnar
artery, it being smaller or absent as the ulnar is larger. It is shown
at _m_, Fig. 123. The radial artery (_g_) now turns gradually dorsad and
passes beneath the tendon of the extensor brevis pollicis onto the
dorsum of the hand. It passes over the oblique groove on the dorsal
surface of the base of the second metacarpal beneath the tendon of the
extensor carpi radialis longus and passes between the bases of the
second and third metacarpals into the palm of the hand. Here it passes
to the ulnar side and anastomoses with the ulnar artery to form the
palmar arch.
=Branches of the Radial Artery.=
1. =A. radialis recurrens= (_i_).--The radial recurrent arises in the
concavity of the elbow and sends a branch proximad to the structures in
the concavity; it then continues to the radial side of the forearm at
the elbow, supplying adjacent parts of the brachialis (2), the extensor
carpi radialis, and the extensor communis digitorum.
2. =A. ulnaris recurrens= (_j_).--The ulnar recurrent arises on the
medial side of the tendon of the biceps and supplies structures in the
concavity of the elbow on the ulnar side, also the pronator teres (5)
and proximal ends of the flexor carpi radialis and flexor profundis
digitorum.
3. =Rami musculares.=--Muscular branches are given off along the course
of the artery, to adjacent muscles. A nutrient artery to the radius
leaves the radial artery about two centimeters distad of the
supracondyloid foramen.
4. =Aa interosseæ= (=anterior= (_l_) and =posterior=) are given off
usually separately between the origin of the ulnar artery and the biceps
tendon. Sometimes they arise as a common trunk which soon divides. The
=posterior interosseous artery= passes distad, supplying the flexor
muscles of the forearm. It also sends a branch to the pronator teres.
The =anterior interosseous= (_l_) may arise from the ulnar artery. It
passes dorsad to the interosseous membrane, on which it runs distad;
sends a nutrient branch to the ulna, and then passes to the wrist in the
substance of the pronator quadratus, which it supplies. It sends a
branch to the dorsal surface of the wrist; this ramifies on the carpus,
forming a network of small arteries.
[Illustration: FIG. 123.--NERVES AND ARTERIES OF THE FOREARM, SEEN
FROM THE FLEXOR SIDE.
Mm. palmaris longus, flexor carpi radialis, flexor carpi ulnaris, and
the third and fourth heads of flexor profundus digitorum have been
removed; also part of M. pronator teres. 1, biceps; 2, conjoined
tendon of brachialis and clavobrachialis; 3, short portion of caput
mediale of triceps brachii; 4, intermediate portion of caput mediale
of triceps brachii; 5, cut ends of pronator teres; 6, brachioradialis;
7, extensor carpi radialis longus and brevis; 8, fifth head of flexor
profundus digitorum; 9, second head of flexor profundus digitorum; 10,
radial part of flexor sublimis digitorum; 11, common tendon of flexor
profundus digitorum; 12, first head of flexor profundus digitorum; 13,
cut origin of flexor carpi ulnaris. _a_, ulnar nerve; _b_, median
nerve; _c_, dorsal cutaneous branch of the ulnar nerve; _d_, palmar
branch of ulnar nerve; _e_, deep palmar branch; _f_, superficial
palmar branch; _g′_, A. brachialis; _g_, A. radialis; _h_, A.
collateralis ulnaris superior; _i_, A. radialis recurrens; _j_, A.
ulnaris recurrens; _k_, A. ulnaris; _l_, A. interossea anterior; _m_,
large branch of A. radialis, joining A. ulnaris.]
5. =A. ulnaris= (_k_).--The ulnar artery passes beneath the second,
third, and fourth parts of the flexor profundus digitorum (but outside
of the origin of the fifth part), to the inner surface of the flexor
carpi ulnaris. It supplies the flexor carpi ulnaris, the flexor
profundus and palmaris longus, and passes on the inner surface of the
flexor carpi ulnaris to the wrist. Near the wrist it sends a branch onto
the side of the forearm, and another to its midventral part, and ends in
a small branch to the wrist on the radial side of the pisiform bone.
This branch anastomoses with the radial to form the palmar arch,
described below.
6. The =palmar arch= (Fig. 124) is formed by the termination of the
radial artery (_a_) in the palm and its junction with the end of the
ulnar (_f_). The radial artery reaches the palm between the bases of the
second and third metacarpals and passes thence toward the ulnar side and
distad, piercing the interosseus muscle of the third digit and lying on
the outer surface of the interossei of the third and fourth digits
beneath the adductors of the second and fifth digits. A small
communicating branch from the radial passes to it between the first and
second metacarpals.
Branches of the palmar arch:
=A. princeps pollicis et indicis= (_c_) leaves the palmar arch near its
radial end and sends a branch onto the ulnar side of the thumb and one
onto the radial side of the index.
The =palmar interosseæ= (_d_) are three in number. They leave the palmar
arch (_b_) and pass distad and dorsad in the intervals between the four
ulnar digits. The radial one passes along the ulnar side of the first
digit, the ulnar one along the radial side of the fifth digit. The
middle one divides and supplies the contiguous sides of the third and
fourth digits. Each of these interosseous arteries sends off muscular
branches (_e_) to the short muscles in the palm, and branches into the
fibrous pad which occupies the palm of the hand. The palmar arch also
sends branches onto the dorsum of the hand at the sides of the fourth
metacarpal. Branches pass from these proximad to the wrist.
B. AORTA ABDOMINALIS. THE ABDOMINAL AORTA.--The abdominal aorta emerges
into the abdomen from between the crura of the diaphragm, at about the
level of the second lumbar vertebra. It passes caudad along the dorsal
middle line, lying to the left of the inferior vena cava. It gives off
=parietal= branches to the body wall, and =visceral= branches to the
viscera, and ventrad of the first sacral vertebra it gives off two
large branches on each side, the =external iliac= (Fig. 126, _k_) and
the =hypogastric= (Fig. 126, _l_)--a very small median vessel, the
=sacralis media= (Fig. 126, _o_), continuing the course of the aorta and
passing into the tail.
The aorta gives off the following branches: =A. cœliaca=; =A.
mesenterica superior=; =Aa. adrenolumbales=; =Aa. renales=; A.
=mesenterica inferior=; =Aa. iliolumbales=; =Aa. lumbales= (seven
pairs); =Aa. iliacæ externæ=; =Aa. hypogastricæ=.
A. =A. cœliaca= (Fig. 125).--The cœliac artery is a large branch which
is given off from the aorta one centimeter or less caudad of the opening
in the diaphragm. It passes directly ventrad about three or four
centimeters, then divides, usually at once, into three branches. The
most cranial of these is the =hepatic= (_d_), the next is the =gastrica
sinistra= (_e_), while the third and largest, seeming to form a
continuation of the cœliac, is the =splenic= (_f_) (=A. lienalis=). The
cœliac artery may give rise also, before its division, to the two
=phrenic= arteries (which, however, usually arise from the
adrenolumbales), and either before or at the point of division to one or
two small =Aa. ventriculi dorsales=, which, however, frequently arise
from the gastrica sinistra.
[Illustration: FIG. 124.