Part 60

This artery (A. maxillaris interna) is much the larger of the two terminal branches of the external carotid. It begins at the inner side of the posterior border of the mandible about two inches (ca. 5 cm.) below the articulation of the jaw and ends in the anterior part of the pterygo-palatine fossa. On account of its complex course and the large number of branches given off it is convenient to divide it into three parts.

The =first part= is much the longest, forms an =S=-shaped curve, and is in great part in contact with the guttural pouch. It passes upward and forward on the inner surface of the mandible a distance of about an inch (ca. 2 to 3 cm.) and is related here to the vein, which is ventral. It then turns inward below the external pterygoid muscle and the inferior maxillary nerve, passes between that muscle and the tensor palati, and runs forward to enter the alar (pterygoid) foramen. This part gives off the following branches:

1. The =inferior alveolar= or =dental artery= (A. alveolaris mandibulæ s. inferior) passes downward and forward with the homonymous vein and nerve, being at first between the external and internal pterygoid muscles, then between the latter and the ramus of the mandible. It enters the mandibular foramen, passes downward and forward in the mandibular canal, and terminates at the mental foramen by dividing into mental and incisor branches. The =mental branch= (A. mentalis) emerges through the mental foramen and anastomoses in the lower lip with the opposite artery and the inferior labial. The =incisor branch= continues forward in the bone, supplies twigs to the canine and incisor teeth, and anastomoses with its fellow of the opposite side. Collateral branches are detached to the pterygoid and mylo-hyoid muscles, and within the bone to the teeth, alveolar periosteum, the gums, and the spongy substance of the mandible.

2. The =pterygoid arteries=, two or three in number, are distributed to the pterygoid and tensor and levator palati muscles.

3. The =tympanic artery= is a very small vessel which passes along the Eustachian tube to the petro-tympanic fissure (of Glaser) and enters the middle ear.

[Illustration:

FIG. 438.—RIGHT EYE OF HORSE.

_a_, Remnants of periorbita; _b_, levator palpebræ superioris; _c_, obliquus oculi inferior; _d_, rectus oculi inferior; _e_, rectus oculi externus; _f_, rectus oculi superior; _g_, sclera; _g′_, cornea; _h_, lacrimal gland; _i_, frontal nerve; _k_, frontal artery; _l_, branch of lacrimal nerve to gland; _m_, lacrimal artery; _n_, zygomatic nerve; _o_, branch of ophthalmic artery; _p_, branch of oculomotor nerve to obliquus oculi inferior; _q_, maxillary nerve; _r_, infraorbital nerve; _s_, posterior nasal nerve; _t_, great palatine nerve; _u_, small palatine nerve; _v_, internal maxillary artery; _w_, buccinator artery (cut); _x_, infraorbital artery; _x′_, malar artery; _y_, sphenopalatine artery; _z_, great palatine artery; _z′_, small palatine (or staphyline) artery; _1_, posterior deep temporal artery; _2_, _3_, stumps of orbital margin; _4_, facial crest; _5_, temporal fossa; _6_, foramen lacerum orbitale; _7_, anterior end of alar canal; _8_, posterior opening of same. (After Ellenberger, in Leisering’s Atlas.) ]

4. The =middle meningeal artery= (A. meningea media) arises beneath the buccinator nerve where the internal maxillary turns forward. It passes backward across the temporal wing of the sphenoid to the antero-external part (foramen spinosum) of the foramen lacerum. Entering the cranium, it divides into branches which course in the grooves on the temporal and parietal bones and supply the dura mater. It anastomoses with the posterior meningeal.

The size of this artery is variable, and is in inverse ratio to that of the posterior meningeal.

5. The =posterior deep temporal artery= (A. temporalis profunda aboralis) arises from the internal maxillary just before the latter enters the canal of the pterygoid process. It passes upward and backward in the temporal fossa on the deep face of the temporalis muscle, in which it ramifies. It sends a branch outward to the masseter, and anastomoses with the superficial temporal and middle meningeal arteries.

In some cases the tympanic and middle meningeal arise from this artery.

The =second part= lies in the alar canal and is about an inch (ca. 2 to 3 cm.) in length. It gives off two branches—the anterior deep temporal and the ophthalmic.

1. The =anterior deep temporal artery= (A. temporalis profunda oralis) emerges from the canal through the temporal or small alar foramen, and passes upward in the anterior part of the temporal fossa on the deep face of the temporalis muscle, in which it is chiefly distributed. It gives twigs to the orbital fat and the skin of the frontal region.

[Illustration:

FIG. 439.—LEFT EYE OF HORSE, DEEPER DISSECTION.

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.

ARTERIES OF THE THORACIC LIMB

THE BRACHIAL ARTERY

The =brachial artery=, after turning around the lower border of the scalenus at the first rib, passes backward and a little downward across the origin of the coraco-brachialis and the insertion of the subscapularis muscle at the inner side of the shoulder joint. At the posterior border of the subscapularis it gives off the subscapular artery, and turns downward on the inner surface of the arm. In its course in the arm it inclines a little forward, crosses the humerus very obliquely, and divides at the antero-internal aspect of the distal third of the shaft of the bone into the anterior and posterior radial arteries.[162]

It is related internally to the serratus magnus and the posterior deep pectoral muscles, and the cubital lymph glands. Externally it lies on the subscapularis, the brachialis, the insertion of the teres major and latissimus dorsi, and the inner head of the triceps. The coraco-brachialis muscle lies along the front of the artery, which, however, overlaps the muscle distally. The vein crosses the inner face of the artery and runs down behind it, accompanied part way by the ulnar and radial nerves. The musculo-cutaneous and median nerves form a loop around the artery close to its origin, and the latter nerve then passes down in front of the artery. The chief branches are as follows:

1. The =suprascapular artery= (A. thoracico-acromialis) is a small and somewhat flexuous vessel, which arises near the anterior border of the subscapularis, runs upward, and dips in between that muscle and the supraspinatus. It gives branches to these muscles, the anterior deep pectoral, and the mastoido-humeralis. A branch passes in front of the coraco-brachialis to the shoulder joint and the proximal end of the humerus.

This vessel may be double, or be represented by one or more branches of the inferior cervical artery.

2. The =subscapular artery= (A. subscapularis) is a very large vessel which arises at the posterior border of the subscapularis muscle. It passes upward in the interstice between that muscle and the teres major on the inner surface of the long head of the triceps, turns around the posterior border of the scapula below the posterior angle, and ends in the infraspinatus and deltoid. Besides collaterals (Rami musculares) to the subscapularis, teres major, triceps, and tensor fasciæ antibrachii it gives off the following named branches:

(_a_) The =thoracico-dorsal= (A. thoracicodorsalis) is a long artery which is usually given off about an inch from the origin of the subscapular, crosses the inner face of the teres major, and runs upward and backward on the latissimus dorsi. It gives branches to these muscles, the abdominal panniculus and the axillary lymph glands.

(_b_) The =posterior circumflex artery= (A. circumflexa humeri posterior) arises a little above the preceding vessel and passes outward behind the shoulder joint between the long and external heads of the triceps with the axillary (or circumflex) nerve. It gives branches to these muscles, the joint capsule, and the muscles and skin of the outer side of the shoulder, anastomosing with the anterior circumflex artery.

(_c_) The =circumflex artery of the scapula= (A. circumflexa scapulæ) arises about two or three inches (ca. 5 to 7.5 cm.) above the shoulder joint, passes forward to the posterior border of the scapula, and divides into two branches. The outer one runs forward on the external surface of the scapula below the spine and gives branches to the supraspinatus, infraspinatus, and teres minor. The inner branch passes forward in a similar fashion on the costal surface of the scapula and supplies branches to the subscapularis.

[Illustration:

FIG. 441.—DISSECTION OF SHOULDER AND ARM OF HORSE, INNER SURFACE.

_A_, Brachial artery; _B_, subscapular artery; _C_, thoracico-dorsal artery; _D_, deep brachial artery; _E_, ulnar artery; _F_, anterior radial artery; _G_, posterior radial (or median) artery; _H_, brachial vein; _I_, external thoracic (or “spur”) vein; _J_, brachial vein; _K_, _K_, _K_, posterior radial veins; _L_, cephalic vein; _L′_, communicating vein; _M_, brachialis muscle; _N_, internal epicondyle of humerus; _O_, prescapular lymph glands; _P_, position of axillary lymph glands; _Q_, position of cubital lymph glands; _1_, suprascapular nerve; _2_, subscapular nerves; _3_, thoraco-dorsal nerve; _4_, musculo-cutaneous nerve; _4′_, cutaneous branch of musculo-cutaneous nerve; _5_, median nerve; _6_, axillary nerve; _7_, ulnar nerve; _8_, radial nerve; _9_, thoracic nerves. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

[Illustration:

FIG. 442.—DISSECTION OF RIGHT FOREARM AND CARPUS OF HORSE, INTERNAL SURFACE.

_C.b._, Coraco-brachialis muscle; _E.m._, internal epicondyle of humerus; _R_, subcutaneous surface of radius. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

3. The =anterior circumflex= (or prehumeral) =artery= (A. circumflexa humeri anterior) arises usually at the upper border of the teres major. It passes forward and outward between the two parts of the coraco-brachialis or between the latter and the humerus. It gives branches to the coraco-brachialis and deep pectoral and ends in the upper part of the biceps and in the mastoido-humeralis. It anastomoses with the posterior circumflex.

Not rarely it arises below the middle of the humerus and passes upward between the biceps and coraco-brachialis. In these cases a small branch for the coraco-brachialis is usually given off at the usual point of origin of the anterior circumflex.

4. The =deep brachial artery= (A. profunda brachii) is a large but short trunk which arises usually about the middle of the humerus. It passes backward and divides into several branches which supply the triceps, tensor fasciæ antibrachii, anconeus, and brachialis. A branch runs in the musculo-spiral groove with the radial nerve to the front of the elbow joint and anastomoses with the anterior radial. A slender branch passes down along the external border of the extensor carpi and supplies cutaneous twigs. Anastomoses occur with the ulnar and recurrent interosseous arteries.

The point of origin is inconstant and it is not uncommon to find two arteries instead. Often a large branch for the posterior deep pectoral muscle is detached close to the origin or arises from the brachial directly.

5. =Muscular branches= (Rami musculares) are distributed to the teres major, deep pectoral, coraco-brachialis, and biceps. The largest and least variable of these supplies the lower part of the biceps.

6. The =ulnar artery= (A. collateralis ulnaris superior) arises a little below the nutrient foramen of the humerus and passes downward and backward along the lower edge of the internal head of the triceps under cover of the brachial vein and the tensor fascia antibrachii. It gives branches to these muscles, the posterior superficial pectoral, the cubital lymph glands, panniculus, and skin. At the internal epicondyle of the humerus it is joined by the ulnar nerve and turns downward under the ulnar head of the flexor carpi medius. It continues with the vein and nerve under the deep fascia of the forearm between the ulnar and humeral heads of the perforans, and in the distal half of the region between the external and middle flexors of the carpus. It unites just above the carpus (under cover of the flexor carpi externus) with a branch of the radial artery, with which it forms the supracarpal arch. It detaches small collaterals to the muscles along which it passes and terminal twigs to the outer surface of the carpus.

7. The =nutrient artery of the humerus= (A. nutritia humeri) is a short vessel which enters the nutrient foramen of the humerus. It often arises from the ulnar.

8. The =anterior radial artery= (A. collateralis radialis inferior) passes downward and a little outward on the anterior face of the humerus under cover of the biceps and brachialis to the front of the elbow joint, where it is joined by the radial nerve. It then descends on the anterior surface of the radius under cover of the anterior extensor of the digit to the carpus, where it concurs in the formation of the rete carpi dorsale, anastomosing with the posterior radial and interosseous arteries. It supplies branches to the elbow joint, the biceps, brachialis, and the extensors of the carpus and digit. A cutaneous branch emerges between the distal end of the biceps and the brachialis.

THE POSTERIOR RADIAL ARTERY

The =posterior radial= or =median artery= (A. mediana) is the direct continuation of the brachial. It passes downward and slightly backward, at first on the inner surface of the humerus, and then over the capsule and internal lateral ligament of the elbow joint, under cover of the posterior superficial pectoral muscle.[163] Below the elbow it dips under the flexor carpi internus and passes down the inner part of the posterior surface of the radius. In the distal part of the forearm it inclines backward and is separated from the radius by the reinforcing band (Caput tendineum) of the superficial flexor of the digit and is continued by the large metacarpal artery.

It is accompanied by the median nerve, which lies in front of the artery at its origin, then crosses over it obliquely at the elbow joint and becomes posterior. In the arm the brachial vein lies behind and partly upon the artery; lower down there are usually two satellite veins, anterior and posterior. The chief collateral branches are as follows:

[Illustration:

FIG. 443.—DISSECTION OF LEFT FOREARM OF HORSE, EXTERNAL SURFACE. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

1. =Articular branches= for the elbow joint.

2. =Muscular branches= to the flexors of the carpus and digit. The largest of these arise at the proximal third of the forearm.

[Illustration:

FIG. 444.—DEEP DISSECTION OF RIGHT CARPUS OF HORSE, POSTERIOR VIEW.

_1_, Radial carpal bone; _2_, accessory carpal bone; _3_, second carpal bone. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

[Illustration:

FIG. 445.—CROSS-SECTION OF RIGHT CARPUS OF HORSE.

The soft structures are cut at the level of the radio-carpal articulation, exposing the proximal row of carpal bones. _Cr_, Radial carpal bone; _Ci_, intermediate carpal bone; _Cu_, ulnar carpal bone; _Ca_, accessory carpal bone. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]