Part 73

The main facts as to the =metacarpal= and =digital arteries= are as follows: The rete carpi dorsale is formed essentially by the terminals of the interosseous artery of the forearm. It gives rise to three =dorsal metacarpal arteries= which descend in the corresponding interosseous spaces and unite with branches of the volar metacarpals to form three =common digital arteries=. Each of these divides into two =proper digital arteries=, which descend along the interdigital surfaces of the digits. On the volar surface are two =volar arches=, superficial and deep, from which three =superficial= and three =deep volar metacarpal arteries= arise. The deep arteries unite near the distal end of the space between the principal metacarpal bones to form a stem which unites with the middle (third) superficial artery. The superficial arteries unite to form an arch from which =proper digital arteries= are given off to the axial aspect of the small digits, and a common digital which supplies two =volar proper digital arteries= to each of the chief digits.

The arteries of the hip, thigh, and leg are arranged much as in the ox. A few special features may be noted.

The =ilio-lumbar artery= gives off a branch to the quadriceps femoris. It may also supply the posterior abdominal artery, which otherwise arises from the deep femoral.

The =deep femoral artery= is given off above the level of the pubis. The posterior abdominal and external pudic arteries may arise from it by a short common trunk or separately. The =external pudic= gives branches to the prepuce but not to the penis. The =popliteal artery= gives off the peroneal.

The =femoral artery= gives off a short trunk which divides into anterior femoral and external circumflex arteries, the latter being much the larger.

The =saphenous artery= is large. It descends on the inner surface of the leg and hock and concurs with the perforating tarsal artery in forming the proximal plantar arch.

The =posterior tibial artery= is small, being replaced distally by the saphenous. It gives branches to the muscles on the posterior face of the tibia and supplies the nutrient artery of that bone.

The =anterior tibial artery= is continued as the dorsalis pedis on the flexion surface of the tarsus. This gives off the =perforating tarsal artery=, which passes back through the vascular canal of the tarsus and unites with the terminal branches of the saphenous to form the proximal plantar arch.

The =metatarsal= and =digital arteries= resemble in arrangement the corresponding vessels of the fore limb.

THE VEINS

The veins resemble in general those of the ox. Thus there is a hemiazygos vein and two jugular veins, the internal one being relatively larger than in the ox. A few differential features may be noted.

The =buccinator vein= resembles that of the horse, and unites with the =vena reflexa= to form a short common trunk which joins the facial.

The =facial vein= resembles in general that of the horse. The =dorsal nasal vein= is large, receives the veins from the snout, runs backward in the groove of the nasal bone and joins the frontal vein; it is connected with its fellow by a transverse branch, and anastomoses freely with the malar and facial.

The veins of the distal parts of the limbs naturally present differences which are correlated with those of the arteries.

THE LYMPH VESSELS AND GLANDS

The =thoracic duct= often divides near its termination into two branches which unite to form an ampulla. The latter suddenly contracts and opens into the terminal part of the left jugular vein.

The =submaxillary lymph glands= are situated in the space between the omo-hyoid and internal pterygoid muscles in relation to the lower part of the anterior border of the submaxillary salivary gland. There are commonly two on each side, one large, the other small.

The =parotid lymph glands= (Fig. 309) are reddish-brown in color. There are usually four of considerable size on either side. One is situated at the upper part of the posterior border of the masseter, partly covered by the parotid gland. Another large subparotid gland lies below the base of the ear. Ventral to this are two smaller glands, one above and one below the external jugular vein.

The =pharyngeal= (or retropharyngeal) =lymph glands= (Fig. 310) are situated on the dorsal wall of the pharynx above the external carotid artery and below and behind the paramastoid process. There are usually two of considerable size on either side.

The =middle cervical lymph glands= form a group on the mastoido-humeralis on the course of the external jugular vein.

The =prescapular lymph glands= are situated at the anterior border of the anterior deep pectoral muscle undercover of the trapezius and omo-transversarius.

The =prepectoral lymph glands= are reddish in color and usually three in number. The largest is placed centrally under the trachea; the others are situated on the brachial vessels as they turn around the first rib.

The =axillary lymph glands= are usually absent, but very small nodes may be found near the insertion of the latissimus dorsi. Cubital glands are not present.

The =thoracic lymph glands= comprise: (1) a gland of considerable size on the first segment of the sternum; (2) about half a dozen reddish glands along the upper face of the thoracic aorta; (3) several glands along the lower face of the trachea; (4) the =bronchial lymph glands=; one of these lies on the bifurcation of the trachea and another at the apical bronchus of the right lung (Fig. 371).

The =lumbar lymph glands= are scattered along the abdominal aorta and the vena cava. Those placed near the hilus of the kidney are often designated =renal=.

The =internal iliac lymph glands= are rounded and relatively large. They comprise: (1) three or four glands situated on and between the origin of the circumflex iliac and the external and internal iliac arteries; (2) a gland in the angle of divergence of the internal iliac arteries.

The =external iliac lymph glands= are small, two or three in number, and lie in front of the circumflex iliac vessels near the point of the hip.

The visceral lymph glands of the abdomen comprise:

1. =Gastric lymph glands= on the lesser curvature of the stomach.

2. Several small =hepatic lymph glands= along the portal vein.

3. An elongated =splenic lymph gland= on the splenic vessels near the dorsal end of the spleen.

4. A series of =mesenteric lymph glands= situated along the anastomotic arches formed by the vessels of the small intestine.

5. Several =cæcal lymph glands= situated along the first part of the cæcal vessels.

6. Two series of =colic lymph glands= which accompany the arteries of the spiral part of the colon, and are exposed by separating the coils of the bowel. Small glands are placed in the colic mesentery and above the rectum.

7. The =anal lymph glands= are situated on either side on the retractor ani.

A small =ischiatic lymph gland= is found on the sacro-sciatic ligament near the lesser sciatic notch.

The =precrural lymph glands= are situated on the aponeurosis of the external oblique below the external angle of the ilium.

The =superficial inguinal lymph glands= are situated behind the external inguinal ring. No deep inguinal lymph glands are present.

The =popliteal lymph glands= are small normally and may escape notice.

A few nodules occur in front of the distal part of the tendo Achillis.

CIRCULATORY SYSTEM OF THE DOG

THE PERICARDIUM AND HEART

The =pericardium= is attached to the sternal part of the diaphragm by a fibrous band, and is connected with the sternum only by the mediastinal pleura.

The =heart= is almost globular in form, the apex being much blunter than in the other animals, and marked by a notch. Its long axis is almost parallel with the sternum and the apex (covered by the pericardium) is directed against the sternal part of the diaphragm. Its weight averages about 0.8 to 1 per cent. of the body-weight.[185]

The base extends forward to a transverse plane through the lower ends of the third pair of ribs. The apex lies opposite the sixth costal cartilage in expiration. On the right side the pericardium is in direct contact with the chest-wall over a narrow triangular area (base anterior) from the fourth to the sixth intercostal space inclusive. On the left side the area of contact is smaller and is at the fourth, fifth, and sixth cartilages.

The two coronary arteries may arise by a common trunk. Each divides into circumflex and descending branches. The left artery is twice as large as the right one.

The great coronary vein ascends in the left longitudinal groove to the coronary groove, in which it winds around the posterior face of the heart to the right side and opens into the right atrium below the posterior vena cava. Near its termination it receives one or two veins which ascend along the right longitudinal furrow. Several small veins from the wall of the right ventricle open into the right atrium separately or by a common trunk.

THE ARTERIES

There is no common brachiocephalic trunk (anterior aorta). Two large vessels arise from the convexity of the aortic arch; these are the =brachiocephalic= and =left brachial arteries=. The =brachiocephalic= gives off the two =carotid arteries=, no common trunk being present. It frequently also supplies the posterior thyroid artery. The intrathoracic branches of the brachial arteries are as follows:

A common trunk gives off the =dorsal=, =subcostal=, and =superior cervical arteries=. The dorsal artery passes out in front of the first rib, and the superior cervical through the first intercostal space. The latter is relatively small.

The =vertebral artery= may arise either in front of or behind the trunk above mentioned; in the latter case it crosses the inner face of the trunk. It passes along the neck in typical fashion to the third cervical vertebra and divides into three branches. The largest of these supplies the muscles in this region, compensating for the absence of branches of the superior cervical artery. The second passes between the second and third cervical vertebræ into the vertebral canal and unites with the opposite artery and a branch of the occipital artery to form the basilar. The third branch is the small continuation of the parent trunk; it passes to the wing of the atlas and anastomoses with the occipital.

The =inferior cervical artery= gives off the superficial cervical which ascends in front of the supraspinatus.

The =internal thoracic artery= is large and sends perforating branches to the pectoral mammary glands.

The =external thoracic artery= arises outside of the thorax and sends branches to the mammary glands.

The =common carotid arteries=, left and right, arise in that order from the brachiocephalic. In the neck the right one lies on the trachea, the left on the œsophagus. Collateral branches are the posterior thyroid (which may, however, arise from the right or left brachial or the inferior cervical), pharyngeal, thyro-laryngeal muscular, tracheal, and glandular (to the submaxillary gland). Each carotid divides under the wing of the atlas into occipital and internal and external carotid branches.

The =occipital artery= is small. It gives off =condyloid= and =posterior meningeal= branches, passes up through the notch on the anterior margin of the wing of the atlas, and is distributed to the muscles of this region. Its =cerebrospinal= branch passes through the intervertebral foramen, and unites in the vertebral canal with its fellow and a branch from the vertebral artery to form the basilar. A retrograde branch anastomoses with the vertebral as in the horse.

The =internal carotid artery=, also small, passes to the foramen lacerum posterius, enters the carotid canal and forms a bend before entering the cranium through the carotid foramen. It forms a plexus which is connected by branches with the middle meningeal and ophthalmic arteries. It then perforates the dura mater and enters into the formation of the arterial circle (of Willis).

The =external carotid artery= is the direct continuation of the common carotid. It passes along the lateral wall of the pharynx, emerges from beneath the digastricus, and divides into superficial temporal and internal maxillary arteries. It gives off the large flexuous =lingual artery= which has a course similar to that of the horse. The =external maxillary=, smaller than the lingual, passes along the upper border of the digastricus, gives off the sublingual, gains the anterior border of the masseter, and divides into superior and inferior labial and the angularis oris. The last-named vessel passes forward on the cheek between the labials to the angle of the mouth. The =sublingual artery= passes at first along the upper border of the digastricus and continues between the mylo-hyoideus and the ramus of the mandible. The =posterior auricular artery= arises at the anterior border of the digastricus, gives branches to the salivary glands and the adjacent muscles, and ascends on the convex face of the concha. It divides into two branches which return along the borders of the external ear.

The =superficial temporal artery=, after giving off the =anterior auricular artery= and a small =transverse facial artery=, turns forward under the temporal fascia toward the eye, and divides into upper and lower branches which supply the frontal region and the eyelids. It also supplies branches to the parotid gland and the masseter and temporalis muscles.

The =internal maxillary artery= pursues a course similar to that of the horse. The mental branches of the =inferior alveolar= (or dental) =artery= are of considerable size and are distributed in the lower lip and gums. Two or three =deep temporal arteries= are present. The anterior one may arise from the buccinator; it gives off the middle meningeal, which sends a branch to the carotid plexus. The =ophthalmic artery= gives off a branch which enters the cranium through the foramen lacerum orbitale and connects with the internal carotid; this is termed the internal ophthalmic and gives off the arteria centralis retinæ. The superficial branches of the =infraorbital artery= replace the dorsal and lateral nasal arteries, and compensate for the small size of the superior labial.

The =brachial artery= in its course in the arm presents no special features. At the elbow it passes between the biceps and the pronator teres, descends (as the median) under the flexor carpi radialis about a third of the way down the forearm, and divides into radial and ulnar arteries. Among its collateral branches are: (1) The =subscapular artery=, which passes up between the subscapularis and teres major, turns around the posterior angle of the scapula and terminates in the supraspinatus, deltoid, trapezius, and mastoido-humeralis. In about half the cases it gives off the =anterior circumflex=, which often arises with the =posterior circumflex=. Its other branches resemble those of the horse. (2) The =anterior circumflex artery= (in about half the cases). (3) The =deep brachial= arises about a third of the way down the arm. (4) The =bicipital artery= (for the biceps) is given off at the lower part of the arm. (5) The =proximal collateral radial artery= (not present in the horse) arises at the lower fourth of the arm, crosses over the terminal part of the biceps, descends on the extensor carpi radialis, and concurs with a branch of the volar interosseous in forming the rete carpi dorsale. It often supplies the bicipital artery. (6) The =anterior radial artery= (A. collateralis radialis distalis) is very small. (7) The =common interosseous artery= is given off a little below the elbow. It supplies branches to the flexor muscles and the =dorsal interosseous artery=, which passes through the interosseous space, gives branches to the extensor muscles, and by its terminal twigs concurs in the formation of the rete carpi dorsale. The direct continuation of the trunk is the =volar interosseous artery=, which descends under cover of the pronator quadratus, gives off a branch to the rete carpi dorsale and the =fifth volar metacarpal artery=, and terminates by joining the volar branch of the radial artery to form the deep volar arch. (8) The =volar antibrachial artery= (Ramus volaris antibrachii) arises below the interosseous and descends at first under the flexor carpi radialis, then between the heads of the deep flexor, and divides into ascending and descending branches.

The =radial artery=, the smaller terminal of the brachial, descends along the inner border of the radius, and divides near the carpus into dorsal and volar branches. The =dorsal branch= assists in forming the rete carpi dorsale. The larger =volar branch= descends behind the inner border of the carpus and joins the end of the volar interosseous in forming the =deep volar arch=. From this arch three =deep volar metacarpal arteries= descend in the second, third, and fourth intermetacarpal spaces and concur with the corresponding superficial volar and the dorsal arteries to form the common digitals.

The =ulnar artery= descends on the deep flexor of the digit, and sends a connecting branch to the radial above the carpus. Near the middle of the metacarpus it gives off the =first volar metacarpal artery= and divides into the =second=, =third=, and =fourth superficial volar metacarpal arteries=. The first volar artery unites with the corresponding dorsal artery to form the =first common digital artery=, which supplies proper digital arteries for the opposed surfaces of the first and second digits. The superficial volar arteries descend in the spaces between the other metacarpal bones, unite near the metacarpo-phalangeal joints with the corresponding deep volar and dorsal metacarpal arteries to form three =common digital arteries=. Each of the latter divides after a short course into two =proper digital arteries=, which run along the opposed surfaces of the second to the fifth digits. The external digital artery of the fifth digit comes from the =superficial volar arch= formed by the union of a branch of the volar interosseous with the fourth superficial volar metacarpal artery.

The rete carpi dorsale gives off four =dorsal metacarpal arteries= which descend in the intermetacarpal spaces and unite near the metacarpo-phalangeal joints with the volar arteries to form the common digitals.

The =thoracic aorta= supplies the last nine or ten pairs of intercostal arteries, but no anterior phrenic arteries. It gives off two or more œsophageal branches, in addition to the broncho-œsophageal, which arises close to or with the sixth intercostal and ramifies in the usual manner.

The =abdominal aorta=, after giving off the external iliac arteries, continues about half an inch to an inch (ca. 1 to 3 cm.) under the last lumbar vertebræ, gives off the internal iliacs, and is continued by the middle sacral artery. This small vessel runs backward under the sacrum and coccygeal vertebræ and gives off branches in segmental fashion.