_a_, Mastoido-humeralis; _b_, sterno-cephalicus; _c_, omo-hyoideus;
_d_, sterno-thyro-hyoideus; _e_, trachea; _f_, position of
cariniform cartilage; _g_, anterior superficial pectoral muscle;
_h_, scalenus; _i_, intertransversales; _k_, insertion of serratus
cervicis; _l_, origin of trapezius; _m_, rhomboideus; _n_, splenius;
_o_, complexus; _p_, _q_, trachelo-mastoideus; _p′_, _q′_, tendons
of same; _r_, longissimus; _s_, obliquus capitis posterior; _t_,
wing of atlas; _u_, parotid gland; _v_, supraspinatus; _w_, anterior
deep pectoral; _x_, spine of scapula; _y_, prescapular lymph glands;
_1_, external maxillary vein; _2_, _3_, jugular vein; _4_, carotid
artery, exposed by drawing jugular vein aside; _5_, _6_, ascending
and descending branches of inferior cervical artery; _7_, cephalic
vein; _8_, branches of superior or deep cervical artery; _9–14_,
ventral branches of second to seventh cervical nerves; _15_,
branches of dorsal divisions of cervical nerves. (Ellenberger-Baum,
Top. Anat. d. Pferdes.)
]
The =right common carotid artery= passes obliquely from the ventral face
of the trachea to its right side. In this position it runs upward and
forward and divides at the crico-pharyngeus muscle and under the
submaxillary gland into external carotid, internal carotid, and
occipital arteries. It is inclosed in a fibrous sheath, and is
accompanied dorsally by the vagus and sympathetic nerves, ventrally by
the recurrent nerve. At the last two cervical vertebræ it is in contact
superficially with the jugular vein, but further forward the
omo-hyoideus muscle intervenes between the artery and vein. Near its
termination the artery becomes more deeply placed and is related
externally to the submaxillary and parotid glands, internally to the
œsophagus. In some cases it is in contact ventrally with the thyroid
gland, especially when the latter is larger than usual.
The =left common carotid artery= differs from the right one in that it
is related deeply to the œsophagus, which separates it from the trachea
in the greater part of its course.
The collateral branches of the common carotids are in the main small.
They comprise:
1. =Muscular branches= (Rami musculares) of variable size, which go to
the ventral muscles of the neck and the skin.
2. =Œsophageal= and =tracheal branches= (Rami œsophagei et tracheales).
Small twigs go to the cervical lymph glands also.
3. The =parotid artery=. This comes off near the termination and enters
the ventral part of the parotid gland. It also supplies the subparotid
lymph glands, and sometimes sends a branch to the submaxillary gland. It
is inconstant.
4. The =thyro-laryngeal artery= (A. thyreoidea cranialis). This, the
largest collateral branch of the carotid, arises from the latter two or
three inches before it divides. It curves over the anterior end of the
thyroid gland, into which it sends several branches. It gives off a
=laryngeal branch= (A. laryngea), which sends twigs to the external
muscles of the larynx and the constrictors of the pharynx, passes
between the cricoid and thyroid cartilages, and supplies the internal
muscles and the mucous membrane of the larynx. A small =pharyngeal
branch= (A. pharyngea ascendens) runs upward and forward to the
crico-pharyngeus, and supplies twigs to the posterior part of the
pharynx and the origin of the œsophagus. Small innominate twigs are
given off to the trachea, the œsophagus, and the sterno-thyro-hyoideus
and omo-hyoideus muscles.
In some cases the thyroid and laryngeal arteries arise from the
carotid separately or by a short common stem. A laryngeal branch is
often detached from the carotid in front of the thyro-laryngeal and
enters the larynx with the superior laryngeal nerve. The pharyngeal
branch frequently comes directly from the carotid.
[Illustration:
FIG. 432.—CROSS-SECTION OF NECK OF HORSE, PASSING THROUGH FIFTH
CERVICAL VERTEBRA; ANTERIOR VIEW.
_a_, Branches of cervical nerves; _a′_, nuchal fat; _b_,
intertransversalis muscle; _c_, longissimus muscle; _d_, vertebral
artery; _e_, vertebral vein; _f_, vertebral nerve; _g_, spinal
accessory nerve (upper division); _h_, recurrent nerve; _i_,
vago-sympathetic trunk; _k_, tracheal lymph duct; _l_, body of fifth
cervical vertebra; _l′_, transverse process of same; _m_, carotid
artery; _n_, jugular vein; _o_, superior cervical artery; _o′_,
satellite vein of _o_; _p_, spinal cord; _q_, dura mater; _r_,
spinal vein; _s_, ligamentum nuchæ; _t_, rhomboideus muscle; _u_,
splenius; _v_, complexus; _w_, multifidus; _x_, serratus cervicis;
_y_, mastoido-humeralis; _z_, sterno-cephalicus; _1_, rectus capitis
ant. major; _2_, omo-hyoideus; _3_, panniculus; _4_,
sterno-thyro-hyoideus; _5_, longus colli; _6_, _7_,
trachelo-mastoideus; _8_, trapezius; _9_, spinalis; _10_, œsophagus;
_11_, trachea, with cartilaginous ring (_11′_), mucous membrane
(_11″_), and muscular layer (_11‴_). (After Ellenberger, in
Leisering’s Atlas.)
]
5. The =accessory thyroid artery= (A. thyreoidea caudalis) is an
inconstant vessel which arises from the carotid at a variable distance
behind the thyro-laryngeal—sometimes from the latter or from the parotid
artery. It sends branches into the posterior part of the thyroid gland
and detaches small tracheal and muscular twigs. In some cases it is
distributed chiefly or entirely to the adjacent muscles.