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THE VEINS OF THE SPINAL MEDULLA.
The veins of the spinal medulla issue from the substance of the spinal medulla, and terminate in a plexus in the pia mater. In that plexus there are six longitudinal channels-one antero-median, along the anterior fissure, two antero-lateral, immediately behind the anterior nerve-roots, two postero-lateral, immediately posterior to the posterior nerve-roots, and one postero-median, dorsal to the posterior septum. Radicular efferent vessels issue from the plexus, and pass along the nerve roots to communicate with the internal vertebral venous network. The veins of the spinal medulla vary very much in size, but they are largest on the lower and on the posterior portions.
The postero-median and antero-median veins are continued above into the corresponding veins of the medulla oblongata.
The antero-lateral and postero-lateral veins pour their blood partly into the median veins and partly into the radicular veins; indeed, the greater part of the blood from the spinal medulla is returned by the radicular veins.
THE VEINS OF THE SUPERIOR EXTREMITY.
The veins of each upper limb are divisible into two sets-viz., superficial and deep. Both sets open eventually into a common terminal trunk which is known as the axillary vein. That vein is, therefore, the chief efferent vein of the upper extremity. It is continued as the subclavian vein to the innominate vein, through which its blood, together with that from the corresponding side of the head and neck, reaches the superior vena cava.
THE DEEP VEINS OF THE UPPER EXTREMITY.
The deep veins of the upper limb, with the exception of the axillary vein, are arranged in pairs, venæ comites, which accompany the different arteries and are similarly named. So far as these veins are concerned it will be sufficient to state that they are provided with valves, that they are situated one on each side of the artery with which they are associated, and that they are usually united together by numerous transverse anastomoses which cross the line of the artery. The axillary vein, however, requires more detailed consideration.
The axillary vein (Figs. 766 and 806) commences, as the direct continuation of the basilic vein, opposite the lower border of the teres major muscle. It passes upwards and medially, through the axilla, along the medial side of the axillary artery, and terminates, at the external border of the first rib, by becoming the subclavian vein. It possesses one or more bicuspid valves of which one is usually situated opposite the lower border of the subscapularis muscle.
Relations. Its anterior relations are similar to those of the axillary artery, but, in addition, the vein is crossed anteriorly, under cover of the clavicular part of the pectoralis major, by the pectoral branches of the thoraco-acromial artery, and by branches of the medial anterior thoracic nerve, and it receives anteriorly, just above the upper border of the pectoralis minor, the termination of the cephalic vein.
Posterior to it are the muscles which form the posterior wall of the axilla, the axillary fat, and the first serration of the serratus anterior. The long thoracic nerve intervenes between it and the serratus anterior, and the subscapular and thoraco-dorsal nerves and the subscapular artery pass between it and the subscapularis.
It is separated from the third part of the axillary artery by the ulnar nerve and medial cutaneous nerves of the forearm; from the second part of the axillary artery by the medial cord of the brachial plexus; and in the proximal part of the axilla, behind the costo-coracoid membrane, it is separated from the first part of the artery by the medial To its medial side lie the lateral set of axillary glands, and, in the distal part of the axilla, the medial cutaneous nerve of the arm.
anterior thoracic nerve.
Tributaries. In addition to tributaries corresponding with the branches of the axillary artery, it receives the venæ comites of the brachial artery, at the lower border of the subscapularis; and the cephalic vein, which joins it above the upper border of the pectoralis minor muscle.
THE SUPERFICIAL VEINS OF THE SUPERIOR EXTREMITY.
The superficial veins of the upper limb commence in the superficial fascia of the palm and dorsum of the hand and of the digits.
The Veins of the Digits and Hand.-The special volar digital veins are two or more fine longitudinal channels which lie in the superficial fascia of the volar
aspects of the digits. They communicate, proximally, with a fine venous network which lies in the superficial fascia of the palm, and, at the proximal ends of the interdigital clefts, by means of intercapitular veins, which pass dorsally between the heads of the metacarpal bones, they open into the special dorsal digital veins. The special dorsal digital veins, two in each digit, anastomose freely together on the dorsal aspects of the digits. At the
Dorsal digital veins proximal ends of
the interdigital clefts they communicate, through the intercapitular veins, with the special volar digi tal veins, and then they unite together to form an indefinite series of dorsal metacarpal veins which terminate,
distal to the middle of the dorsum of the hand, in a dorsal venous arch. The Veins of the Forearm and Arm.-The veins of the forearm emerge from the dorsal venous arch and from the volar venous plexus, and they vary considerably in number and in size. As a rule there are two main longitudinal channels, the cephalic vein on the radial side and the basilic vein on the ulnar side. In some cases there is an additional median vein on the volar aspect of the forearm.
The cephalic vein commences in the radial end of the dorsal venous arch. It receives the metacarpal veins of the thumb, turns round the radial margin of
the distal part of the forearm, and runs proximally, parallel with the volar border of the brachioradialis muscle, to the cubital region. There, frequently much reduced in size, it turns laterally and runs, along the lateral border of the prominence
of the biceps, to the interval between the Costo-coracoid membrane
a few cases instead of piercing the costocoracoid membrane it crosses the front of the clavicle, deep to the platysma, pierces the deep cervical fascia, and joins the lower part of the external jugular vein.
As it runs proximally, on the volar aspect of the forearm, a number of tributaries join its lateral border. Some of these commence in the dorsal venous arch of the hand and others in the superficial fascia of the dorsal aspect of the forearm.
In the cubital region it is connected with the basilic vein by a large obliquely placed anastomosing channel, the median cubital vein, which runs along the medial border of the distal part of the biceps prominence, superficial to the lacertus fibrosus which separates it from the distal part of the brachial artery. In the delto-pectoral triangle it is joined by tributaries which correspond with the acromial and pectoral branches of the thoraco-acromial artery.
The median cubital vein not only connects together the cephalic and basilic veins but it receives also the profunda vein which pierces the deep fascia and connects it with the deep veins of the forearm, and one or more superficial veins, of varying size which pass, proximally, along the volar aspect of the forearm.
In many cases the median cubital vein is relatively very large, and in such cases the more proximal part of the cephalic vein, which lies in the arm, is a comparatively small vessel.
The basilic vein commences in the ulnar end of the dorsal venous arch of the hand. It runs along the dorsal aspect of the forearm to the junction of the proximal and middle thirds, where it turns round the ulnar border of the forearm, and runs, anterior to the medial epicondyle of the humerus, to the medial bicipital groove. At the middle of the arm, it pierces the deep fascia. After piercing the fascia, it runs proximally, along the medial border of the brachial artery, to the axilla, and there becomes the axillary vein.
As it runs proximally, in the forearm, it is joined by tributaries from both the volar and dorsal aspects and, in the cubital region, by the median cubital
vein which connects it with the cephalic vein.
The Median Vein of the Forearm.-In a certain number of cases a vein, which commences in the palmar venous plexus, runs along the middle of the volar aspect of the forearm to the cubital region. It is called the median vein of the forearm. At the bend of the elbow it receives the profunda vein and then divides into two branches, the median cephalic and the median basilic veins (Fig. 791). The median cephalic vein runs along the lateral bicipital sulcus and joins the cephalic vein. The median basilic passes along the medial bicipital sulcus and joins the basilic vein. When the median vein of the forearm is present the median cubital vein is absent.
When venesection is performed in the fore
arm it is either the median cubital vein or, in its absence, the median basilic vein which is opened.
VENA CAVA INFERIOR AND ITS TRIBUTARIES.
The inferior vena cava (Fig. 792) is a large venous trunk which receives the whole of the blood from the lower extremities, and the greater part of the blood from the walls and contents of the abdomen and pelvis. It commences opposite the right side of the body of the fifth lumbar vertebra, behind and to the right of the right common iliac artery. It ascends through the abdomen, anterior and to the right of the vertebral column and the right crus of the diaphragm, and it pierces the cupola of the diaphragm, between the middle and right sections of the central tendinous leaflet, at the level of the lower part of the eighth thoracic vertebra. It then enters the middle mediastinum, pierces the fibrous pericardium, and terminates in the lower and posterior part of the right atrium. Its intra-thoracic portion is very short, and its intra-pericardial portion, which is still shorter, is covered anteriorly and on its right and left sides by the parietal portion of the serous layer. Attached to the inferior and anterior margin of its atrial orifice is the valve of the inferior vena cava (Eustachian). This is a remnant of an important fold of endocardium by which, in the foetus, the blood from the inferior vena cava is directed, through the foramen ovale, into the left atrium.
Relations. The inferior vena cava is in relation, posteriorly, with the bodies of the
lower lumbar vertebræ and the corresponding part of the anterior longitudinal ligament, the anterior portion of the right psoas major muscle, the right lumbar sympathetic trunk, the roots of the right lumbar arteries, the right crus of the diaphragm, the right renal artery, the right suprarenal artery, the right coeliac ganglion, the right inferior phrenic artery, and the medial and upper portion of the right suprarenal gland.
Anterior to it, from below upwards, are the following structures the right common iliac artery, the lower end of the mesentery and the superior mesenteric artery, the right
internal spermatic artery and the third part of the duodenum, the head of the pancreas, the portal vein and the first part of the duodenum, the foramen epiploicum, and the posterior surface of the liver. More superficially are coils of small intestine, the great omentum, and the transverse colon and mesocolon.
To its left side are the aorta and the right crus of the diaphragm.
On its right side, below, is the right ureter, whilst at a higher level the right kidney is separated from the vein by a short interval only.
Tributaries. In addition to the two common iliac veins, by the union of which it is formed, and through which it receives blood from the pelvis and from the lower extremities, the inferior vena cava receives the following tributaries:-The hepatic veins, the