The outer plate of bone has been removed behind the pterygoid crest to
expose the vessels and nerves. _a_, _a_, Remnants of periorbita;
_b_, stump of rectus oculi superior; _c_, obliquus oculi inferior;
_d_, rectus oculi inferior; _e_, rectus oculi lateralis; _e′_,
retractor oculi; _f_, rectus oculi internus; _g_, _g_, obliquus
oculi superior; _h_, eyeball; _i_, trochlear nerve; _k_, ophthalmic
nerve; _k′_, nasal nerve; _k″_, infratrochlear nerve; _k‴_,
ethmoidal nerve; _l_, optic nerve; _m_, frontal nerve; _n_, lacrimal
nerve; _o_, zygomatic nerve; _p_, nerve to obliquus inferior (from
oculomotor); _q_, maxillary nerve; _r_, infraorbital nerve; _s_,
sphenopalatine nerve; _t_, great palatine nerve; _u_, small palatine
nerve; _v_, internal maxillary artery; _w_, buccinator artery (cut
off); _x_, infraorbital artery; _x′_, malar artery; _y_,
sphenopalatine artery; _z_, great palatine artery; _z′_, small
palatine (or staphyline) artery; _1_, _2_, stumps of zygomatic arch;
_3_, stump of supraorbital process; _4_, facial crest; _5_, temporal
fossa; _6_, ophthalmic artery; _7_, muscular branch of _6_; _8_,
lacrimal artery (cut); _9_, frontal artery; _10_, anterior deep
temporal artery; _11_, ethmoidal artery. (After Ellenberger-Baum,
Top. Anat. d. Pferdes.)
]
2. The =ophthalmic artery= (A. ophthalmica externa) emerges from the
anterior opening of the alar canal, and enters the apex of the
periorbita or ocular sheath. Within this it forms a semicircular bend
under the rectus oculi superior and is continued by the ethmoidal
artery. Its branches are as follows:
(_a_) The =supraorbital= or =frontal artery= (A. supraorbitalis)[161] is
a small vessel which often arises from the anterior deep temporal or the
internal maxillary. It passes along the inner wall of the orbit in
company with the nerve of the same name to the supraorbital foramen,
through which it emerges. It is distributed to the orbicularis oculi,
the corrugator supercilii, and the skin of the supraorbital region.
(_b_) The =lacrimal artery= (A. lacrimalis) runs upward and forward
within the periorbita along the outer edge of the levator palpebræ
superioris to the lacrimal gland, in which it is chiefly distributed. It
also sends twigs to the upper eyelid.
(_c_) =Muscular branches= (Rami musculares) supply the orbital muscles,
the periorbita, the third eyelid, and the conjunctiva.
(_d_) =Ciliary branches= (Aa. ciliares), two sets of very slender
arteries, arise from the ophthalmic direct and from the muscular
branches. The anterior ciliary arteries (Aa. ciliares anteriores) pierce
the sclera in front of the equator and ramify chiefly in the ciliary
body and the iris. The posterior ciliary arteries (Aa. ciliares
posteriores) pierce the posterior part of the sclera; most of them
ramify in the choroid coat as the short ciliary arteries, but two of
larger size, the long ciliary arteries, run forward, one on each side,
between the sclera and choroid to the periphery of the iris. Here they
divide into branches which anastomose and form a circle (Circulus iridis
major). From this secondary branches are detached which form a second
circle around the pupil (Circulus iridis minor).
[Illustration:
FIG. 440.—SAGITTAL SECTION OF HEAD OF HORSE, CUT A LITTLE TO THE RIGHT
OF THE MEDIAN PLANE.
_1_, Skin; _2_, nasal bone; _3_, frontal bone; _4_, parietal bone;
_4′_, tentorium osseum; _5_, occipital bone; _6_, sphenoid bone;
_7_, hard palate; _8_, premaxilla; _9_, mandible; _10_, hyoid bone;
_11_, septum between frontal sinuses; _12_, alar cartilage; _13_,
dilatator naris transversus; _14_, septum nasi with venous plexuses;
_15_, palato-labial artery; _16_, _16′_, upper and lower septal
branches of _15_; _17_, septal branch of sphenopalatine artery and
satellite vein; _18_, septal branch of ethmoidal artery; _19_,
sphenoidal sinus; _20_, guttural pouch; _21_, pharynx; _22_,
pharyngeal orifice of Eustachian tube; _23_, posterior naris; _24_,
soft palate; _25_, palatinus muscle; _26_, pharyngeal muscles; _27_,
œsophagus; _28_, dotted line indicating position of posterior pillar
of soft palate; _29_, lamina; _29′_, arch of cricoid cartilage;
_30_, arytenoideus transversus muscle; _31_, epiglottis; _32_, body
of thyroid cartilage; _33_, vocal process and cord; _34_, arytenoid
cartilage; _35_, lateral ventricle of larynx; _36_, trachea; _37_,
ventral straight muscles of head; _38_, longus colli; _39_, atlas;
_40_, axis; _41_, lig. nuchæ; _42_, dorsal spinal muscles; _43_,
muscles of external ear; _44_, omo- and sterno-hyoideus; _45_,
tongue; _46_, mylo-hyoideus; _47_, genio-hyoideus; _48_,
genio-glossus; _49_, longitudinalis inferior; _50_, longitud.
superior; _51_, hyo-epiglotticus; _52_, chin and mentalis muscle;
_53_, venous plexus of hard palate; _54_, corpus callosum; _55_,
septum pellucidum; _56_, fornix; _57_, thalamus; _58_, pineal body;
_59_, corpora quadrigemina; _60_, cerebral peduncle; _61_, corpus
mammillare; _62_, pituitary body; _63_, chiasma opticum; _64_,
intercarotid artery; _65_, medulla oblongata; _66_, interventricular
foramen; _67_, infundibulum; _68_, third ventricle; _69_, cerebral
aqueduct; _70_, anterior medullary velum; _71_, fourth ventricle;
_72_, posterior medullary velum; _73_, basilar artery; _74_, spinal
cord; _75_, ethmoidal nerve; _76_, septal branch of posterior nasal
nerve; _76′_, branch of same to organ of Jacobson; _77_, olfactory
nerve to organ of Jacobson; _78_, nasal branches of palatine artery.
(After Ellenberger, in Leisering’s Atlas.)
]
(_e_) The =central artery of the retina= (Arteria centralis retinæ) is a
small vessel which arises from the ophthalmic or from a posterior
ciliary artery. It pierces the optic nerve a short distance behind the
sclera and runs in its center to the lamina cribrosa, where it breaks up
in thirty to forty fine branches. These appear in the fundus of the eye
at the margin of the optic papilla and radiate in the posterior part of
the retina.
(_f_) The =ethmoidal artery= (A. ethmoidalis) is the continuation of the
ophthalmic. It enters the cranial cavity through the ethmoidal foramen,
passes inward on the cribriform plate, and divides into meningeal and
nasal branches. The former ramify in the anterior part of the dura mater
and anastomose with branches of the artery of the corpus callosum. The
nasal branch passes through the cribriform plate, gives branches to the
mucous membrane of the lateral mass of the ethmoid and the adjacent part
of the septum nasi, and runs forward on the superior turbinal.
The =third part= passes forward in the pterygo-palatine fossa,
accompanied by branches of the maxillary nerve. On reaching the
posterior palatine foramen it is continued by the palatine artery. Its
branches are as follows:
(1) The =buccinator artery= (A. buccinatoria) arises from the lower
aspect of the internal maxillary shortly after its emergence (Fig. 437).
It turns around the maxillary tuberosity, accompanied by the buccinator
nerve, and under the masseter muscle, enters the cheek, and runs forward
in it. It supplies branches to the cheek, the superior buccal glands,
and the masseter and pterygoid muscles. Near its origin it gives off a
branch to the orbital fat behind the periorbita.
(2) The =infraorbital= or =superior dental artery= (A. infraorbitalis)
arises from the upper aspect of the internal maxillary a little in front
of the preceding vessel. It passes upward and forward to the maxillary
foramen, runs in the infraorbital canal in company with the nerve of the
same name, and is continued forward within the jaw to the incisor teeth.
It gives branches to the teeth and gums, and detaches a branch through
the infraorbital foramen which anastomoses with the lateral nasal and
superior labial. About midway between its origin and the maxillary
foramen it gives off the =malar= or =orbital branch= (Ramus malaris),
which passes along the floor of the orbit to end in the lower lid and
anastomose with the angularis oculi. It gives twigs to the inferior
oblique muscle and the lacrimal sac.
The infraorbital artery is usually small at its emergence upon the
face, but in some cases it is rather large and may partially replace
the superior labial and lateral nasal arteries.
(3) The =staphyline= or =small palatine artery= (A. palatina minor) is a
small vessel which passes forward in the groove at the inner side of the
maxillary tuberosity to the soft palate. In the groove it is accompanied
by the nerve of the same name and the palatine vein.
(4) The =sphenopalatine artery= (A. sphenopalatina) arises in the
extreme anterior part of the pterygo-palatine fossa and passes into the
nasal cavity, where it divides into internal and external branches. The
internal branch is distributed to the mucous membrane of the septum
nasi; the external one goes to the inferior turbinal, the inferior
meatus, the posterior nares, and the maxillary and frontal sinuses. It
may arise from the infraorbital.
(5) The =palatine= or =palato-labial artery= (A. palatina major) is the
direct continuation of the internal maxillary. It passes through the
palatine canal to the roof of the mouth, accompanied by the palatine
nerve, and runs forward in the palatine groove, where it is joined by
the vein. A little behind the plane of the corner incisor teeth it
curves inward over a bar of cartilage to the foramen incisivum, where it
unites with its fellow of the opposite side. The single artery thus
formed passes up through the foramen and divides under the transverse
dilator of the nostril into two branches. These ramify in the upper lip
and anastomose with the lateral nasal and superior labial arteries. In
its course in the roof of the mouth the palatine artery gives off
branches to the hard and soft palate and the gums, and others which pass
through the accessory palatine foramina to be distributed in the mucous
membrane of the lower part of the nasal cavity. Commonly two branches,
right and left, are detached from the convexity of the arch formed by
the union of the two arteries; these run forward in the anterior part of
the hard palate.