Part 186

(2) The =pharyngeal artery=, which, however, often arises from the occipital.

(3) The =posterior auricular=, which resembles that of the horse and sends a stylo-mastoid branch into the tympanum. It may arise from the superficial temporal.

(4) The =masseteric artery= resembles that of the horse, but is smaller.

The =superficial temporal artery= is large and presents the following special features: (1) Its transverse facial branch passes into the central part of the masseter. (2) It gives off a branch which corresponds to the posterior meningeal artery of the horse, enters the temporal canal, and ramifies in the dura mater, giving off twigs to the external ear, the temporal muscle, and the frontal sinus. (3) It usually gives off the anterior auricular artery. (4) Branches are supplied to the frontalis muscle and the eyelids, (5) A large branch passes around the outer side of the base of the horn-core, supplies the matrix of the horn, and anastomoses across the back of the frontal eminence with the artery of the opposite side.

The =internal maxillary artery= is less curved than in the horse and is entirely extraosseous, since the alar canal is absent. The principal differential features in its branching are as follows:

(1) The =ophthalmic artery= forms a rete mirabile within the periorbita. Its frontal branch enters the supraorbital canal and ramifies chiefly in the frontal sinus.

(2) Several branches take the place of the internal carotid artery. One of these enters the cranial cavity through the foramen ovale and several small ones pass through the foramen which represents the foramen rotundum and foramen lacerum orbitale of the horse. They concur with the vertebral and condyloid arteries in the formation of an extensive =rete mirabile= on the cranial floor around the sella turcica. From each side of the rete an artery arises which is distributed in general like the internal carotid of the horse.

(3) The =malar artery= is large; it arises by a common trunk with the infraorbital and gives off the =dorsal nasal= and the =angular artery of the eye=.

(4) The =infraorbital artery= is large and emerges from the infraorbital foramen to form the =lateral nasal artery=.

(5) The =palatine artery= is smaller than in the horse and usually arises by a common trunk with the sphenopalatine. It passes through the palatine canal and along the palatine groove, enters the nasal cavity through the incisive fissure, and does not go to the upper lip. It forms a rete mirabile about the naso-palatine canal and terminates in the mucous membrane of the anterior part of the nasal cavity.

ARTERIES OF THE THORACIC LIMB

The =brachial artery= pursues the same course in the arm as that of the horse. At the elbow it becomes the median. The chief differential features in its branches are as follows:

1. The =subscapular artery= is almost as large as the continuation of the brachial. The =posterior circumflex artery= sends branches backward and downward into the triceps, taking the place in part of the deep brachial artery. The =thoracico-dorsal artery= supplies branches to the pectoral muscles and the triceps as well as the teres major and latissimus dorsi; it may arise directly from the brachial.

2. The =deep brachial artery= is small.

3. The =superior collateral ulnar artery= is often double, and does not extend to the carpus.

The =median artery= (posterior radial artery) descends along the inner part of the posterior surface of the radius and divides near the middle of the forearm into the radial and ulnar arteries. It gives off at the upper third of the forearm the =common interosseous artery=, a large vessel which anastomoses with the deep brachial, passes through the proximal interosseous space, and descends (as the dorsal interosseous) in the groove between the radius and ulna, and concurs in the formation of the rete carpi dorsale. At the distal end of the forearm it sends a branch through the distal interosseous space, which passes downward, assists in forming the rete carpi volare, and is continued in the metacarpus as the external deep volar metacarpal artery. This is a small vessel which passes down under the outer border of the suspensory ligament and assists in forming the deep volar arch near the fetlock.

FIG. 470.—ARTERIES OF DISTAL PART OF RIGHT FORE LIMB OF OX, ANTERIOR VIEW.

a, Interosseous artery; b, dorsal branch of radial artery; c, rete carpi dorsale; d, dorsal metacarpal artery; e, dorsal common digital artery; f, f, dorsal proper digital arteries. ]

FIG. 471.—ARTERIES OF DISTAL PART OF RIGHT FORE LIMB OF OX, POSTERIOR VIEW.

g, Ulnar artery; h, radial artery; i, volar branch of common interosseous artery; k, l, m, deep volar metacarpal arteries; A.v., volar arches; n, volar common digital artery; o, o′, p, volar proper digital arteries. ]

The =radial artery= is smaller than the ulnar. It descends on the flexor carpi internus, passes over the postero-internal surface of the carpus, and is continued as the internal deep volar metacarpal. At the distal end of the forearm and at the carpus it furnishes branches to the retia carpi. Another branch (A. met. perforans proximalis) runs outward between the suspensory ligament and the large metacarpal bone, passes through the proximal foramen of the bone, and unites with the interosseous artery; before passing through the foramen it detaches the middle deep volar metacarpal artery (A. met. volaris prof. III.), which descends on the posterior face of the metacarpal bone, receives an anastomotic branch from the internal deep artery, and concurs in the formation of the deep volar arch above the fetlock.

The =ulnar artery=, the larger of the two divisions of the median, descends under cover of the flexor carpi internus without giving off any large branches in the forearm. It passes through the carpal canal and continues along the inner side of the deep flexor tendon as the =volar common digital artery=. At the distal third of the metacarpus this vessel is joined by a branch from the internal deep volar metacarpal artery, forming the superficial volar arch. Near this another branch of the common digital (or of the internal digital) passes around the outer border of the flexor tendons to the posterior face of the metacarpal bone and concurs with the deep volar metacarpal arteries in the formation of the deep volar arch. A branch from the arch passes forward through the inferior foramen of the metacarpal bone and joins the dorsal metacarpal artery which descends from the rete carpi dorsale in the anterior metacarpal groove.

The =volar common digital artery= (A. metacarpea volaris superficialis III.) passes into the interdigital space and divides into two =volar proper digital arteries=, which descend along the interdigital surfaces of the chief digits and pass through the foramina at the upper part of the interdigital surfaces of the third phalanges, enter the cavities in these bones, and ramify in a manner similar to the corresponding vessels in the horse. The volar common digital detaches a branch (A. interdigitalis perforans) which passes forward through the upper part of the interdigital space and anastomoses with the dorsal metacarpal artery.

The volar proper digital arteries (or the common digital) give off, in addition to other collaterals, branches which correspond to the arteries of the plantar cushion of the horse. These pass to the bulbs of the claws and anastomose with each other and with the inner and outer digital arteries, forming an arch from which numerous branches are distributed to the matrix of the hoofs.

The =dorsal metacarpal artery= (A. met. dorsalis III.) is a small vessel which arises from the rete carpi dorsale, descends in the groove on the anterior face of the metacarpal bone, and is joined by the inferior perforating metacarpal artery from the deep volar arch to constitute the dorsal common digital artery. This vessel (A. digitalis communis dorsalis III.) divides into two =dorsal proper digital arteries=.

The =internal digital artery= (A. digiti III. medialis) is the continuation of the internal deep volar metacarpal artery. It descends on the inner side of the inner digit and terminates at the bulb of the claw by anastomosing with the corresponding volar proper digital artery. It gives off a branch to the rudimentary digit and forms a transverse anastomosis behind the first phalanx with the volar common digital or its inner division.

The =external digital artery= (A. digiti IV. lateralis) arises from the deep volar arch, passes down on the outer side of the external digit and is distributed like the inner one.

BRANCHES OF THE THORACIC AORTA