Part 171

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.) ]

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. 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:

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.

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.) ]

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.) ]

3. The =common interosseous artery= (A. interossea communis) is a vessel of considerable size which arises at the level of the interosseous space, through which it passes. Before entering the space it gives off a small branch, the volar interosseous (A. interossea volaris), which descends to the radial head of the perforans. In the space it supplies the nutrient arteries of the radius and ulna. Emerging from the space it gives off branches to the flexor carpi externus, a small =recurrent branch= (A. interossea recurrens) which passes upward on the outer surface of the ulna and anastomoses with the deep brachial and ulnar arteries, and is continued as the =dorsal interosseous artery=. This vessel (A. interossea dorsalis) passes down between the anterior and lateral extensors of the digit and concurs with the anterior radial in forming a network on the anterior surface of the carpus, the =rete carpi dorsale=. From the latter arise two small vessels, the =internal= and =external dorsal metacarpal arteries= (A. metacarpea dorsalis medialis, lateralis), which run distally in the grooves between the large and small metacarpal bones and anastomose with the volar metacarpal arteries.

4. The =artery of the rete carpi volare= (A. retis carpi volaris) is a small vessel which arises at the distal third of the forearm and passes downward to the posterior surface of the carpus, where it concurs with branches of the volar metacarpal arteries in forming the rete carpi volare.

5. The =external volar metacarpal artery= (A. metacarpea volaris lateralis) is a small vessel which arises just above the carpus under cover of the flexor carpi medius and anastomoses with the ulnar artery, forming the supracarpal arch. From the latter a branch descends with the outer branch of the median nerve, inclines outward toward the posterior border of the accessory carpal bone, and arrives at the head of the external metacarpal bone. Here it is connected with the internal volar metacarpal artery, usually by two transverse branches, thus forming the =deep volar= or =subcarpal arch= (Arcus volaris profundus). One of these branches lies between the subcarpal check ligament and the suspensory ligament; the other (not always present) lies beneath the latter on the large metacarpal bone. A small branch descends to the fetlock with the external metacarpal nerve. Below the arch the artery pursues a flexuous course downward on the posterior face of the large metacarpal bone alongside of the external small metacarpal and under cover of the suspensory ligament. At the distal third of the metacarpus it commonly unites with the corresponding vessel of the inner side to form a short trunk which passes backward through the angle of divergence of the branches of the suspensory ligament and joins the external digital or the common digital artery.

FIG. 446.—CROSS-SECTION OF MIDDLE OF RIGHT METACARPUS OF HORSE.

a, Common digital (or large metacarpal) artery; b, internal metacarpal vein; c, internal metacarpal nerve; d, external metacarpal nerve; e, branch of external volar metacarpal artery; f, external metacarpal vein; g, g, g, deep volar or interosseous metacarpal arteries; h, tendon of anterior extensor; i, tendon of lateral extensor; k, anastomotic branch connecting metacarpal nerves; l, deep flexor tendon; m, check ligament; n, superficial flexor tendon; o, suspensory ligament; p, large metacarpal bone; q, q, small metacarpal bones; r, skin (After Ellenberger, in Leisering’s Atlas.) ]

6. The =internal volar= or =small metacarpal artery= (A. metacarpea volaris medialis) is given off from the posterior radial at an acute angle, usually a little above the external one or by a common trunk with it. It passes down the inner side of the carpus behind the tendon of the flexor carpi internus and embedded in the posterior annular ligament. Arriving at the proximal end of the inner metacarpal bone it becomes more deeply placed and is connected with the external volar artery by one or two transverse branches as stated above. It then pursues a flexuous course downward alongside of the inner small metacarpal bone, like the corresponding external artery, with which it commonly unites as described above. It is larger than the external artery and supplies the nutrient artery to the large metacarpal bone.