1. =Aa. coronariæ.=--The coronary arteries are two. They arise from the
aortic sinuses. The left one (Fig. 118, _p_) leaves the aorta on the
left side, passes dorsad of the pulmonary artery, and divides into two
branches, one of which follows the auriculoventricular groove (sulcus
coronarius) to the dorsal side of the heart and sends branches to the
adjacent heart-walls, while the other runs onto the ventricles,
following approximately the ventral border of the ventricular septum.
The _right coronary_ artery passes in the auriculoventricular groove
toward the right and dorsad, and supplies the adjacent walls of the
heart.
2. =A. anonyma= (Fig. 115, _j_; Fig. 118, _b_).--The innominate artery
passes craniad from the convexity of the aortic arch (_a′_). It gives
rise first to a small =mediastinal artery= (_m_) which passes ventrad
into the mediastinum, then to the =left common carotid= (Fig. 115, _l_),
then to the =right common carotid= (Fig. 115, _m_). Sometimes the
carotids are given off from a common trunk. Beyond the right common
carotid the innominate is continued as the =right subclavian= (Fig. 115,
_n_).
[Illustration: FIG. 118.--VESSELS OF THE THORAX, VIEWED FROM THE LEFT
SIDE.
_a_, aorta (_a′_, aortic arch); _b_, innominate artery; _c_, left
subclavian; _d_, right subclavian; _e_, right common carotid; _f_,
left common carotid; _g_, costocervical axis; _g′_, vertebral artery;
_h_, internal mammary artery; _i_, axillary artery; _j_, thyrocervical
axis; _k_, A. transversa scapulæ; _m_, mediastinal artery; _n_,
intercostal arteries; _o_, œsophageal arteries; _p_, left coronary
artery; _q_, superior vena cava; _r_, internal mammary vein; _s_, the
two innominate veins; _t_, sternal artery; _u_, costocervical vein;
_v_, vertebral vein; _w_, axillary vein; _x_, vein to clavotrapezius
and lateral ends of the pectoral muscles; _y_, vein accompanying
second branch of A. transversa scapulæ; _z_, thyrocervical vein. 1,
external jugular vein; 2, internal jugular vein; 3, vena cordis magna;
4, œsophagus; 5, thoracic duct; 6, one of the lymphatic ducts from the
neck. _I_, first rib (cut); _VIII_, eighth rib (cut); _XII_, twelfth
rib (cut).]
3. =A. subclavia sinistra= (Fig. 115, _k_; Fig. 118, _c_).--The left
subclavian passes craniad from the convexity of the aortic arch. It
curves about the first rib (Fig. 118, _I_) to enter the armpit, where it
becomes the =axillary artery= (_i_).
4. =Aa. intercostales= (_n_).--The intercostal arteries are given off
from the dorsal side of the aorta. Each passes to an intercostal space
and divides into three branches. One of these passes ventrad along the
caudal margin of the cranial one of the two ribs between which it
extends. Another goes to the deep muscles of the back, and the third
enters the spinal canal through the intervertebral foramen. The arteries
for the first and second (and sometimes the third) intercostal space
usually arise from the subclavian (costocervical axis, Fig. 118, _g_).
5. =Aa. bronchiales.=--The bronchial arteries are two, and arise either
from the aorta opposite the fourth intercostal space or from the fourth
intercostal arteries. They accompany the bronchi to the lungs.
6. =Aa. œsophageæ= (Fig. 118, _o_).--The œsophageal arteries are small
branches of varying origin passing to the œsophagus.
7. =Aa. lumbales.=--The lumbar arteries correspond to the intercostals,
but pass off between the lumbar vertebræ. The obliquity of the diaphragm
throws the origin of one or two pairs of them within the thorax.
A. CAROTIS COMMUNIS. THE COMMON CAROTID ARTERY. (Fig. 115, _l_ and _m_;
Fig. 119, _a_).
The two common carotid arteries arise from the innominate artery in the
manner already described. Each passes craniad along the side of the
trachea. In the thorax (Fig. 118, _f_) the common carotid lies mediad of
the subclavian artery (Fig. 118, _c_) and dorsad of the superior vena
cava (Fig. 118, _q_). In the neck (Fig. 119) the artery lies,
accompanied by the vagus and sympathetic nerves and the internal jugular
vein (_b_), in the space between the longus capitis muscle (7) and the
trachea (14); it is covered ventrally by the sternomastoid and
sternothyroid (2) muscles, lying close to the lateral border of the
latter. Near its origin the common carotid may give rise to the small
=inferior thyroid= artery. It then passes to about the level of the
larynx without giving off branches; here it gives off the =superior
thyroid= (_c_) on the ventral side and one or more muscular branches
(_e_) on the dorsal side. One or two centimeters further craniad it
gives off on the dorsal side the =internal carotid= (_g_) and the
occipital artery (_f_). The main artery now takes the name =external
carotid= (_m_).
[Illustration: FIG. 119.--COMMON CAROTID ARTERY AND INTERNAL JUGULAR
VEIN.
_a_, common carotid artery; _b_, internal jugular vein; _c_, superior
thyroid artery; _d_, cervicalis ascendens artery; _e_, large muscular
branches; _f_, occipital artery; _g_, internal carotid; _h_, branch to
larynx; _i_, lingual artery; _j_, external maxillary; _k_, superior
labial; _l_, inferior labial; _m_, external carotid; _n_, internal
maxillary; _o_, posterior auricular; _p_, superficial temporal. 1, M.
sternohyoideus; 2, M. sternothyreoideus; 3, M. geniohyoideus; 4. M
genioglossus; 5, M. constrictor pharyngis medius; 6, M. constrictor
pharyngis inferior; 7, M. longus capitis; 8, M. digastricus; 9, M.
masseter; 10, M. scalenus; 11, M. levator scapulæ (cut); 12, M.
levator scapulæ ventralis (cut); 13, M. splenius; 14, trachea.]
Branches of the common carotid:
1. =A. thyreoidea ima.=--The inferior thyroid is a small artery which
arises either from the common carotid near its origin, or from the
innominate before the origin of the carotid. It passes craniad on the
trachea as far as the thyroid gland, giving branches to the trachea and
œsophagus.
2. =A. thyreoidea superior= (_c_).--The superior thyroid leaves the
carotid opposite the thyroid cartilage and passes mediad and caudad,
sending branches to the thyroid gland, and the sternothyroid (2) and
sternohyoid (1) muscles. A small branch, the =superior laryngeal=,
passes to the larynx, and supplies those muscles of the larynx which are
not enclosed by the cartilages.
3. =Rami musculares= (_e_).--One or two branches, usually of
considerable size, leave the common carotid at about the same level as
the superior thyroid and pass to the muscles on the dorsal side of the
neck, the main trunk of the artery passing between the longus capitis
(7) and scalenus muscles (10).
4. =A. occipitalis= (_f_).--The occipital artery arises from the common
carotid at about the same point as the internal carotid. It immediately
sends a large branch dorsad, passing between M. longus capitis (7) and
the vertebral column, to the deep muscles of the neck. The occipital
then crosses the outer surface of the digastric muscle (8) to the back
of the skull, and runs along the lambdoidal crest just beneath the
splenius muscle. It sends a number of branches to the muscles of the
back of the neck; and one of its branches may unite with the vertebral
artery as it lies in the groove on the atlas, or with a branch of the
vertebral.
5. =A. carotis interna= (_g_).--The internal carotid artery is one of
the terminal branches of the common carotid. It is very small. It is
given off near or in common with the occipital artery, passes toward the
cranial end of the tympanic bulla, enters the bulla with the Eustachian
tube, and passes into the skull at the foramen lacerum. Its course is
much convoluted before entering the foramen. Within the skull (Fig. 121,
_g_) it joins the posterior cerebral artery (Fig. 121, _f_) at the side
of the hypophysis.
6. =A. carotis externa= (Fig. 119, _m_).--After giving off the internal
carotid the continuation of the common carotid artery receives the name
=external carotid= (_m_). It passes craniad and laterad between the
digastric (8) and styloglossus muscles, where it gives off cranioventrad
the =lingual artery= (_i_) and a number of small muscular branches; also
sometimes the small =laryngeal= artery. At the dorsolateral border of
the digastric (8) it gives off the =external maxillary= artery (_j_),
and about one centimeter farther craniad the =posterior auricular=
(_o_). It now turns mediad, lying against the cartilaginous auditory
meatus, on its cranial side, and gives off the =superficial temporal=
(_p_). The artery then continues mediad, taking the name =internal
maxillary= (_n_)--so that the internal maxillary artery is to be
considered the terminal branch of the external carotid.
Branches of the external carotid artery (Fig. 119):
_a._ =A. lingualis= (Fig. 119, _i_; Fig. 120, _d_).--The lingual artery
leaves the external carotid near its beginning and passes craniomediad
along the ventral border of the digastric muscle (Fig. 120, 9),
accompanied by the hypoglossal nerve. It gives off numerous small
branches to the hyoid and pharyngeal muscles, then passes dorsad of the
hyoglossus muscle (Fig. 120, 6), where it gives off a branch which
passes transversely across the middle line to communicate with the
artery of the other side. Beneath the hyoglossus the artery turns
craniad and passes into the tongue. Here it runs along the medial border
of the styloglossus to the tip of the tongue, giving off numerous
branches into the substance of this organ.
_b._ =Rami musculares.=--Muscular branches pass to the digastric and to
the hyoid muscles. A small branch (Fig. 119, _h_), which may arise
either from the external carotid or from the common carotid near the
beginning of the external carotid, passes to the larynx and supplies the
thyroarytenoid and lateral cricoarytenoid muscles of the larynx.
_c._ =A. maxillaris externa= (Fig. 119, _j_).--The external maxillary
artery leaves the external carotid (_m_) opposite the angle of the jaw
and at about the dorsal border of the digastric muscle (8). It passes
craniad, lying at first beneath the digastric muscle and sending a
branch to the submaxillary gland. Opposite the caudal border of the
mylohyoid muscle it gives off the =submental= artery, turns dorsad,
emerges from beneath the digastric, and passes along the cranial border
of the masseter onto the face. Here it divides into =superior= (_k_) and
=inferior= (_l_) =labial= branches, which pass along the upper and lower
lips, respectively, giving off numerous branches.
The =submental= artery passes to the symphysis menti between the
digastric and mylohyoid muscles, giving off on its course collateral
branches to the muscles of this region.
_d._ =A. auricularis posterior= (Fig. 119, _o_).--The posterior
auricular leaves the external carotid (_m_) opposite the middle of the
bulla tympani and beneath the submaxillary gland. It passes about the
base of the ear on its caudal and dorsal sides outside of the deep
muscles of the occipital region, but beneath the auricular muscles, and
sends several branches to the muscles of the external ear, passing onto
the caudal surface of the concha. It sends also a large branch mediad
to the muscles of the occiput, especially to the temporal muscle, within
which it ramifies. A large branch (=anterior auricular=, Fig. 131, _u_)
passes from the caudal side of the concha craniodorsad, and appears on
the cranial side of the external ear, running along the cranial margin
of the auditory opening.
_e._ =A. temporalis superficialis= (Fig. 119, _p_; Fig. 120, _h_).--The
superficial temporal artery arises from the external carotid as the
latter lies between the cartilaginous auditory meatus and the caudal
border of the masseter muscle. It passes dorsad and gives off soon after
its origin a muscular branch to the masseter, and an =auricular= branch
which passes distad along the concha auris and ramifies over its cranial
surface. The superficial temporal itself passes onto the surface of the
temporal muscle (Fig. 120, 11), to which it gives numerous branches. It
extends to the caudal angle of the eye (Fig. 131, _s_), where it
divides. One branch passes into the lower eyelid; the larger branch
passes along the dorsal side of the eye, sending a branch into the orbit
and small branches onto the dorsal surface of the nose.
_f._ =A. maxillaris interna= (Fig. 119, _n_; Fig. 120, _i_).--The
internal maxillary artery is the continuation of the external carotid.
It turns caudad at the caudal end of the mandible, then passes craniad,
lying dorsad of the pterygoid muscles (Fig. 120, 10), and against the
medial surface of the mandible. It gives off the =inferior alveolar=
artery (Fig. 120, _j_), then the =middle meningeal= (_k_), and then
continuing mediad divides into three or four branches. The branches
redivide, and the twigs form a complicated plexus, the =carotid plexus=
(Fig. 120, _l_), which surrounds the maxillary division of the fifth
nerve near its exit from the foramen rotundum. One of the larger
branches of the plexus enters the skull through the orbital fissure,
lying beside the hypophysis; it divides in the manner described below.
[Illustration: FIG. 120.--BRANCHES OF EXTERNAL CAROTID ARTERY.
_a_, common carotid; _b_, branch to larynx; _c_, internal carotid;
_d_, lingual; _e_, external carotid; _f_, posterior auricular; _g_,
external maxillary; _h_, superficial temporal; _i_, internal
maxillary; _j_, inferior alveolar; _k_, middle meningeal; _l_, carotid
plexus; _m_, branch to temporal muscle; _n_, ophthalmic; _o_,
infraorbital; _p_, lesser palatine. 1, M. constrictor pharyngis
inferior; 2, M. sternothyreoideus; 3, M. sternohyoideus; 4, M.
thyreohyoideus; 5, M. constrictor pharyngis medius; 6, M. hyoglossus;
7, M. geniohyoideus; 8, M. genioglossus; 9, M. digastricus; 10, Mm.
pterygoidei externus and internus (cut); 11, M. temporalis (cut).]
Beyond the carotid plexus a main trunk which may be considered the
continuation of the internal maxillary passes craniad, lying on the
dorsal surface of the external pterygoid muscle; nearly opposite the
molar tooth it divides into the =infraorbital= (Fig. 120, _o_) and the
=sphenopalatine= arteries.
Branches of the internal maxillary artery and of the carotid plexus:
1. =A. alveolaris inferior= (Fig. 120, _j_).--The inferior alveolar (or
inferior dental) artery leaves the inferior maxillary just opposite the
condyloid process of the mandible. It enters the mandibular canal by the
mandibular foramen, along with the nerve of the same name, and traverses
the canal, furnishing branches to the lower teeth. It emerges at the
mental foramen, and its terminal branches are distributed to the chin,
but a branch is continued in the bone beyond the mental foramen and
supplies the incisor and canine teeth of the lower jaw.
2. =A. meningea media= (Fig. 120, _k_).--The middle meningeal is a large
vessel which leaves the internal maxillary at about the same level as
the inferior alveolar. It passes into the foramen ovale and ramifies in
the dura mater. Its branches leave distinct impressions on the inner
surface of the bones of the skull.
3. A large branch (Fig. 121, _h_) from the plexus passes into the
cranial cavity through the orbital fissure and lies within the skull at
the side of the hypophysis. It gives off the following branches:
_a._ A =posterior communicating= branch, very short, which extends
caudad and joins the internal carotid artery (Fig. 121, _g_).
_b._ =A. cerebri media= (Fig. 121, _i_).--The middle cerebral artery
passes dorsad on the side of the cerebral hemisphere along the fissure
of Sylvius and divides into numerous branches which are distributed to
the surface of the cerebrum.
_c._ =A. cerebri anterior= (Fig. 121, _j_) Passes dorsad between the
cerebral hemispheres. Just craniad of the optic chiasma the two anterior
cerebral arteries are united by a small communicating branch, thus
completing the circulus arteriosus or circle of Willis (Fig. 121),
surrounding the hypophysis (see page 292).
4. From the carotid plexus several branches pass, arising either
separately or in common, to the masseter, temporal, and pterygoid
muscles.
5. =A. ophthalmica= (Fig. 120, _n_).--The ophthalmic artery passes from
the carotid plexus to the structures in the orbit. It gives off
numerous branches which supply the muscles of the eyeball, and other
structures of this region. It sends an =ethmoidal= branch into the nasal
cavity through the ethmoidal foramen in the orbital plate of the frontal
bone, then continues distad to emerge from the orbit on the medial side
of the eye; here it anastomoses with branches of the superficial
temporal.
6. =A. palatina minor= (Fig. 120, _p_).--The lesser palatine artery
leaves the internal maxillary distad of the carotid plexus, near the
caudal border of the maxillary bone. It passes ventrocaudad into the
soft palate.
7. =A. sphenopalatina.=--The sphenopalatine is one of the terminal
branches of the internal maxillary; it passes mediad through the
sphenopalatine foramen into the nasal cavity, and divides into numerous
branches which supply the mucous membrane of the nose. It gives off just
before it enters the sphenopalatine foramen the =descending palatine=
(=A. palatina descendens=), which passes into the posterior palatine
canal and emerges on the surface of the hard palate, where it ramifies.
8. =A. infraorbitalis= (Fig. 120, _o_).--The infraorbital artery is a
direct continuation craniad of the internal maxillary. It sends off
numerous small branches to the teeth of the upper jaw, and a rather
large branch which passes to the lower eyelid. It then enters the
infraorbital foramen, at the same time dividing usually into two or
three branches; these emerge from the foramen and supply the parts of
the nose and upper lip adjacent to the foramen (Fig. 131, _r_).