Part 170

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) 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).

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.

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.