258 CIRCULATORY SYSTEM. 



From the arrangement of these sinuses, it appears that each 

 bone of the spine has its own venous system or circle; which 

 also is the case in regard to the corresponding section of me- 

 dulla spinalis in early life, when it occupies the whole length 

 of the spine. Each of these circles, by the freedom of their 

 anastomoses, therefore, forms a link in a long chain of venous 

 circles belonging to the structure of the spine. 



SECT. II. OF THE VEINS OF THE UPPER EXTREMITIES. 



The veins of the upper extremities are superficial and deep- 

 seated, and arise from the distribution of the arteries. 



The Deep-sealed Veins are found in company with each ar- 

 terial ramification, there being two veins to one artery gene- 

 rally. We thus have them observing the course of the arteries 

 of the hand, of the fore arm, of the arm, and of the shoulder. 

 At the bend of the arm, the two radial and the two ulnar veins 

 coalesce into the two brachial veins, which attend the brachial 

 artery, one on each of its sides, and at intervals throw anasto- 

 motic branches across it. Sometimes, but one of these trunks 

 exists, with the exception of the lower part of the arm, where 

 there are most commonly two. The trunk (or trunks, as the 

 case may be,) is joined by the basilic vein, at a point varying 

 from .the middle of the arm to the axilla. These venae comites, 

 or satellites, are invariably called after the arteries which they 

 attend, and having no difference from the latter in relative si- 

 tuation, a farther description of them may be dispensed with. 



The Superficial Veins lie between the skin and the brachial 

 aponeurosis, and are considerably larger than the preceding. 

 Their earliest roots are seen on the back of the fingers; they 

 then appear on the back of the hand, on the posterior face of 

 the lower end of each interosseous space. There are common- 

 ly six trunks in all: the one on the ulnar side of the hand, and 

 the three next to it, converge towards the middle of the back 

 of the carpus into a single trunk; the two others, one of which 

 comes from the thumb and the other from the back of the fore- 

 finger, converge to the outer end of the carpus, and there form 

 a single trunk also. Between these several trunks, there are 



