THE AXILLAEY VEIN. 977 



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 poster o-lateral, immediately 

 posterior to the posterior nerve -roots, and one poster v- 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-rnedian 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, venae 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. 



VENA AXILLARIS. 



The axillary vein (Eigs. 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 

 1 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 

 anterior thoracic nerve. To its medial side lie the lateral set of axillary glands, and, 

 m the distal part of the axilla, the medial cutaneous nerve of the arm. 



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