Part 61

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.

[Illustration:

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.

The foregoing account describes the most common arrangement of the dorsal and volar metacarpal arteries. Variations in their origin and connections are common, but have no great surgical importance. Collateral branches are omitted for the same reason. In some cases the internal volar metacarpal is connected with the common digital or large metacarpal artery a little below the carpus by a branch passing obliquely across the inner border of the deep flexor tendon; this forms a superficial volar arch.

THE COMMON DIGITAL ARTERY

[Illustration:

FIG. 447.—DISSECTION OF RIGHT CARPUS, METACARPUS, AND DIGIT OF HORSE, INNER VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

The =common digital= or =large metacarpal artery=[164] is the direct continuation of the posterior radial. It descends in the carpal canal along the inner side of the flexor tendons in company with the inner branch of the median nerve and a satellite vein. Continuing down the limb it preserves this relation to the tendons to the distal third of the metacarpus, where it inclines toward the middle line of the limb behind the suspensory ligament, and divides into the internal and external digital arteries. In the metacarpus the artery is related to the vein in front and the artery behind, and is covered by the fascia and skin. It furnishes collateral branches to the suspensory ligament, the flexor tendons, and the skin.

THE DIGITAL ARTERIES

The =internal= and =external digital arteries= (A. digitalis medialis, lateralis) are formed by the bifurcation of the common digital at the distal third of the metacarpus. They diverge, pass down over the outer surface of the corresponding sesamoid at the fetlock, and descend parallel with the borders of the deep flexor tendon to the volar grooves and foramina of the third phalanx. Entering the latter the two arteries unite in the semilunar canal and form the =terminal arch= (Arcus terminalis), from which numerous branches pass through the bone to the wall surface and ramify in the matrix of the wall and sole of the hoof. A number of branches emerge through the foramina at the lower border, where they anastomose with each other in arciform fashion. These branches were named by Spooner the inferior communicating arteries, and the anastomotic arch formed by them is termed the circumflex artery of the third phalanx (Chauveau) or the artery of the lower border of the third phalanx (Leisering).

Each artery is accompanied by a vein and by the digital nerves. Above the fetlock the artery is most deeply placed and is covered by the vein; the nerve is behind the vein. At the fetlock the artery has become superficial and is related to the vein in front and the posterior branch of the nerve behind. The anterior branch of the nerve crosses over the artery obliquely to the lateral aspect of the first phalanx. The vessels and nerves are crossed obliquely by a small tendinous band, the ligament of the ergot, which begins in the fibrous basis of the ergot at the back of the fetlock and extends downward and forward to end in the fascia at the side of the pastern joint.

In addition to branches to the joints, tendons and synovial sheath, ergot, and skin, the digital arteries give off:

1. The =artery of the first phalanx= or perpendicular artery (A. phalangis primæ), a short trunk which arises at a right angle about the middle of the first phalanx, and divides into dorsal and volar branches (Rami dorsales et volares). The dorsal (anterior) branch passes between the first phalanx and the extensor tendon and ramifies on the front of the digit, anastomosing with its fellow. The volar (posterior) branch dips in between the flexor tendons and the inferior sesamoidean ligaments and anastomoses with the opposite artery.

2. The =artery of the plantar cushion= (A. toricæ phalangis tertiæ) arises at the proximal border of the lateral cartilage and passes backward and downward to ramify in the plantar cushion and the matrix of the heels and frog.

3. The =dorsal artery of the second phalanx= (Ramus dorsalis phalangis secundæ) arises a little above the navicular bone, and passes forward under cover of the lateral cartilage and the extensor tendon to the front of the second phalanx, where it anastomoses with the opposite vessel. It gives branches to the skin, the tendon, the coffin joint, and the coronary matrix of the hoof.

4. The =volar artery of the second phalanx= (Ramus volaris phalangis secundæ) is smaller than the preceding, opposite to which it arises. It passes above the proximal border of the third sesamoid and unites with the opposite artery.

The arteries of the second phalanx form what is termed by Chauveau the =coronary circle=. The dorsal (anterior) part of the circle gives off commonly an artery (A. coronalis phalangis tertiæ) near either side of the extensor tendon, which divides into two branches. The central branch unites with that of the opposite side, while the other joins a branch of the artery of the plantar cushion. In this way is formed the =circumflex artery of the coronary cushion=, an anastomotic arch which lies on the extensor tendon at the coronet. In some cases descending branches of the arteries of the first phalanx concur in the formation of the arch.

5. The =dorsal artery of the third phalanx= or preplantar artery (A. dorsalis phalangis tertiæ) arises at the deep face of the wing of the third phalanx, passes outward through the notch or foramen there, and runs forward in the groove on the wall surface. It gives off ascending and descending branches, which ramify in the matrix of the wall of the hoof, anastomosing above with the circumflex artery of the coronary cushion and below with the circumflex artery of the third phalanx. Before passing through the wing it detaches a retrograde branch to the plantar cushion, and after emerging one which ramifies on the outer aspect of the lateral cartilage.

The terminal part of the digital artery after giving off the preceding vessel is sometimes termed the plantar.

BRANCHES OF THE THORACIC AORTA

In addition to the coronary arteries and the common brachiocephalic trunk (which have been described), the thoracic part of the aorta gives off branches to the thoracic walls and viscera and to the spinal cord and its membranes. The =visceral branches= (Rami viscerales) are the bronchial and œsophageal, which arise by a broncho-œsophageal trunk. The =parietal branches= (Rami parietales) are the intercostal and phrenic arteries.

1. The =broncho-œsophageal= (Truncus broncho-œsophageus) is a short, usually bulbous, trunk which arises at the sixth thoracic vertebra from the aorta or in common with the first aortic intercostal arteries. It passes (under cover of the vena azygos) down the right face of the aorta toward the bifurcation of the trachea and divides into bronchial and œsophageal branches.

(_a_) The =bronchial artery= (A. bronchialis) crosses the left face of the œsophagus to the bifurcation of the trachea, where it divides into right and left branches. Each enters the hilus of the corresponding lung above the bronchus, which it accompanies in its ramification. It supplies the lung tissue and also detaches twigs to the bronchial lymph glands and the mediastinum.

(_b_) The =œsophageal artery= (A. œsophagea) (Fig. 429) is a small vessel which passes backward above the œsophagus in the posterior mediastinum and anastomoses with the œsophageal branch of the gastric artery. It detaches twigs to the œsophagus and the mediastinal lymph glands and pleura, and also gives off two branches which pass between the layers of the ligaments of the lungs and ramify in the subpleural tissue. Very commonly there is another artery which runs backward ventral to the œsophagus.

In some cases there is no broncho-œsophageal trunk, the bronchial and œsophageal arising separately. In other cases the second aortic intercostal arises in common with them also.

2. The =intercostal arteries= (Aa. intercostales) (Figs. 428, 429) number eighteen pairs. The first arises from the deep cervical artery, the next three from the subcostal branch of the dorsal artery, and the remainder from the aorta. The aortic intercostals arise from the dorsal face of the aorta in pairs close together; the fifth and sixth usually spring from a common stem. Each passes across the body of a vertebra to the corresponding intercostal space, detaches twigs to the vertebræ and the pleura, and divides into dorsal and ventral branches. The =dorsal branch= (Ramus dorsalis) gives off a spinal branch (Ramus spinalis) which passes through the intervertebral foramen, gives twigs to the membranes of the spinal cord, perforates the dura, and reinforces the ventral spinal artery. A muscular branch passes to the muscles and skin of the back. The =ventral branch= (Ramus ventralis) is much the larger. It passes downward, at first almost in the middle of the intercostal space between the intercostal muscles, then gains the posterior border of the rib and is subpleural. Each is accompanied by a vein and nerve, the artery being in the middle and the vein in front. At the lower part of the space it unites with a ventral intercostal branch of the internal thoracic or the asternal artery. It supplies the intercostal muscles, the ribs and the pleura, and gives off perforating branches which pass out to the serratus magnus, the abdominal muscles, and the skin.

3. The =phrenic arteries= (Aa. phrenicæ) are two or three small vessels which arise at the hiatus aorticus from the ventral aspect of the aorta, often by a common trunk. They supply the crura of the diaphragm. In some cases they arise in common with an intercostal artery.

BRANCHES OF THE ABDOMINAL AORTA

The collateral branches of the abdominal part of the aorta are distributed chiefly to the walls and contents of the abdominal cavity, but some branches are supplied to the spinal cord and its membranes, and others extend into the pelvis and to the scrotum. The =visceral branches= are the cœliac, anterior mesenteric, renal, posterior mesenteric, and the spermatic or utero-ovarian. The =parietal branches= are the lumbar arteries.

[Illustration:

FIG. 448.—PLAN OF BRANCHES OF CŒLIAC ARTERY OF HORSE.

_1_, Cœliac artery; _2_, gastric artery; _3_, hepatic artery; _4_, splenic artery; _5_, posterior gastric artery; _6_, anterior gastric artery; _7_, œsophageal branch; _8_, gastro-duodenal artery; _9_, pancreatico-duodenal artery; _10_, right gastro-epiploic artery; _11_, pyloric artery; _12_, left gastro-epiploic artery; _13_, short gastric branches of splenic. ]

I. The =cœliac artery= or =axis= (A. cœliaca) is an unpaired vessel, usually half an inch or less (ca. 1 cm.) in length, which arises from the ventral aspect of the aorta at its emergence from the hiatus aorticus. It divides on the dorsal surface of the pancreas into three branches—the gastric, hepatic, and splenic.

1. The =gastric artery= (A. gastrica sinistra) passes downward and forward in the gastro-phrenic ligament, gives off œsophageal and pancreatic branches, and divides above and behind the cardia into anterior and posterior branches.

(_a_) The =anterior branch= (Ramus cranialis) crosses the lesser curvature just to the right of the cardia and ramifies on the parietal surface of the stomach. The branches pursue a flexuous course toward the greater curvature and anastomose with the short gastric arteries and the gastric branch of the hepatic artery.

(_b_) The =posterior branch= (Ramus caudalis) is distributed in a similar fashion on the visceral surface.

(_c_) The =œsophageal branch= (Ramus œsophageus) passes through the hiatus œsophageus into the thoracic cavity above the œsophagus and anastomoses with the œsophageal branch of the broncho-œsophageal artery.

[Illustration:

FIG. 449.—PLAN OF CHIEF BRANCHES OF ANTERIOR MESENTERIC ARTERY OF HORSE.

_1_, Stump of anterior mesenteric artery; _2_, stumps of arteries of small intestine; _3_, external cæcal artery, _4_, internal cæcal artery; _5_, ileal artery; _6_, ventral colic artery; _7_, dorsal colic artery; _8_, middle colic or first artery of small colon. ]

The gastric artery often arises by a common trunk with the splenic. The two terminal branches may arise separately, or the anterior from the splenic and the posterior from the hepatic. The œsophageal branch often arises from the splenic or the posterior gastric.

[Illustration:

FIG. 450.—DISSECTION OF SUBLUMBAR REGION, PELVIC INLET, AND INNER SURFACE OF THIGH OF HORSE.

_Blood-vessels_: _1_, Aorta; _2_, posterior vena cava; _3_, hepatic; _4_, gastric; _5_, splenic; _6_, _7_, renal; _8_, anterior mesenteric; _9_, arteries of small intestine; _10_, ileo-cæco-colic; _11_, dorsal colic; _12_, artery of small colon; _13_, posterior mesenteric; _14_, external iliac; _15_, internal iliac; _16_, circumflex iliac; _17_, _19_, anterior and posterior branches of _16_; _18_, anastomosis with intercostals; 20, spermatic; _21_, cremasteric; _22_, lateral sacral; _23_, internal pudic; _24_, umbilical; _25_, femoral; _26_, deep femoral; _27_, anterior femoral; _28_, branch to gracilis; _29_, saphenous.

_Lymph vessels and glands_: _a_, Lymph vessels; _b_, lumbar glands; _c_, internal iliac glands; _d_, external iliac glands; _e_, precrural glands; _f_, deep inguinal glands (position indicated by dotted line).

_Nerves and ganglia_: _1_, _2_, Left and right cœliaco-mesenteric ganglia; _3_, posterior mesenteric ganglion; _4_, connection between _1_ and _2_; _5_, connection between hepatic and splenic nerves; _6_, _7_, connections between anterior and posterior mesenteric ganglia; _8_, splanchnic nerve; _9_, lumbar trunk of sympathetic; _10_, pelvic branches of posterior mesenteric ganglion; _11_, internal spermatic nerve; _12_, last thoracic nerve; _13_, ilio-hypogastric nerve; _14_, anastomosis between _13_ and _15_, ilio-inguinal nerve; _16_, _17_, cutaneous and muscular branches of _15_; _18_, _19_, muscular and scrotal branches of external spermatic nerve; _20_, external cutaneous nerve of thigh; _21_, femoral nerve; _22_, saphenous nerve; _23_, branch of _22_ to sartorius.

_A_, Cut surface of obliquus abdominis externus; _B_, cut surface of obliquus abdominis internus; _C_, depression due to disappearance of fat in interval between outer border of psoas major and iliacus; _D_, thick part of iliac fascia which extends from tendon of psoas minor to external angle of ilium; _E_, superficial fascia of flank; _F_, internal inguinal ring; _G_, external inguinal ring; _H_, patella; _I_, femoral canal; _J_, semimembranosus; _K_, suspensory ligaments of penis; _L_, cross-section of penis; _M_, stump of spermatic cord; _N_, ilio-psoas; _O_, tensor fasciæ latæ; _P_, _P_, extremities of external angle of ilium; _Q_, remains of iliac fascia; _R_, ilio-lumbar ligament or deep layer of lumbo-dorsal fascia; _S_, line of attachment of gastro-pancreatic fold; _T_, tendon of right crus of diaphragm; _U_, right crus; _V_, aorta at hiatus aorticus; _W_, left crus of diaphragm. The position of the kidneys is indicated by dotted lines. (After Schmaltz, Atlas d. Anat. d. Pferdes) ]

2. The =hepatic artery= (A. hepatica) is larger than the gastric. It passes forward to the right and ventrally on the dorsal surface of the pancreas, covered by the gastro-pancreatic fold, crossing obliquely under the vena cava, and reaches the inner border of the portal vein. It divides into three or four branches which enter the portal fissure of the liver and ramify within the gland with the portal vein and the hepatic duct. It gives off the following collateral branches:

(_a_) =Pancreatic branches= (Aa. pancreaticæ) are given off as the artery crosses the pancreas, in which it is partly embedded.

(_b_) The =pyloric artery= (A. gastrica dextra) arises above the first curve of the duodenum. It descends to the pylorus, sending branches to the first part of the duodenum and the pylorus, and anastomoses with the gastric and right gastro-epiploic arteries. It may arise from the gastro-duodenal.

(_c_) The =gastro-duodenal artery= (A. gastroduodenalis) passes to the second curve of the duodenum and divides into the right gastro-epiploic and the pancreatico-duodenal. The =right gastro-epiploic artery= (A. gastroepiploica dextra) crosses over the posterior surface of the duodenum and enters the great omentum, in which it runs to the left, parallel with the greater curvature of the stomach. It gives branches to the latter and to the omentum and forms an anastomotic arch with the left gastro-epiploic artery. The =pancreatico-duodenal artery= (A. pancreaticoduodenalis) divides into pancreatic and duodenal branches. The former (Ramus pancreaticus) supplies the middle part of the pancreas and is often replaced by a number of variable twigs. The duodenal branch (Ramus duodenalis) passes to the right along the lesser curvature of the duodenum and anastomoses with the first branch of the anterior mesenteric artery.

3. The =splenic artery= (A. lienalis) is the largest branch of the cœliac. It passes to the left (with the large satellite vein) on the left extremity of the pancreas and across the saccus cæcus of the stomach. Entering the suspensory ligament of the spleen, it runs in the hilus of the spleen to the apex, beyond which it is continued as the left gastro-epiploic. It gives off the following branches:

(_a_) =Pancreatic branches= (Rami pancreatici) to the left extremity of the pancreas.

(_b_) =Splenic branches= (Rami lienales), which plunge into the substance of the spleen.

(_c_) =Gastric branches= (Aa. gastricæ breves), which pass in the gastro-splenic omentum to the greater curvature of the stomach, where they bifurcate and anastomose with the gastric arteries.

(_d_) The =left gastro-epiploic artery= (A. gastroepiploica sinistra) is the continuation of the splenic artery. It passes to the right in the great omentum, parallel with the greater curvature of the stomach, and anastomoses with the right gastro-epiploic. It gives off branches to the greater curvature of the stomach, and twigs to the omentum.

II. The =anterior= or =great mesenteric artery= (A. mesenterica cranialis) arises from the ventral face of the aorta at the first lumbar vertebra. It is a large unpaired trunk, about an inch (ca. 2 to 3 cm.) in length, which passes ventrally between the vena cava and the left adrenal into the root of the great mesentery, when it divides into three branches—left, right, and anterior.[165]

1. The =left branch= gives off at once about fifteen to twenty =arteries of the small intestine= (Aa. intestinales).[166] These come off close together and pass in divergent fashion between the layers of the great mesentery, each dividing into two branches which anastomose with adjacent branches to form a series of arches. In the anterior part of the series secondary arches are formed by the union of branches given off from the primary set of arches. From the convex side of these arches terminal branches pass to the wall of the small intestine, in which they ramify and form a vascular network. They are accompanied by satellite veins and by nerves and lymph vessels. The first artery anastomoses with the pancreatico-duodenal, and the last with the ileal branch of the great mesenteric artery. Branches are supplied to the mesenteric lymph glands.

2. The =right branch= (A. ileo-cæco-colica) might be regarded as the continuation of the trunk. It runs downward and a little forward and to the right and gives off the ileal, the two cæcal, and the ventral colic arteries.

(1) The =ileal= or =ileo-cæcal artery= (A. ilea) passes in retrograde fashion along the terminal part of the ileum and unites with the last branch of the left division.

(2) The =external= or =inferior cæcal artery= (Ramus cæcalis lateralis) passes between the cæcum and the origin of the colon and runs on the external muscular band of the cæcum to the apex, where it anastomoses with the internal artery. Besides numerous collaterals to the cæcum, it gives off the artery of the arch, which passes along the lesser curvature of the base of the cæcum and runs on the outer face of the origin of the great colon.

(3) The =internal= or =superior cæcal artery= (Ramus cæcalis medialis) passes along the inner band to the apex of the cæcum, where it anastomoses with the external cæcal artery.

(4) The =ventral=, =right=, or =direct colic artery= (A. colica ventralis) runs along the opposed surfaces of the ventral (first and second) parts of the great colon to the pelvic flexure, where it unites with the dorsal colic artery. It supplies the ventral parts of the great colon and sends a branch to the base of the cæcum.