THE ANTEMIOB VENA CAVA. 611 



metacarpus. A number of muscular and subcutaneous branches enter tliis 



vein. 



It has the same origin as the posterior radial veins. Its superior or 

 terminal extremity bends forward, close to the trunk of the epioondyloid 

 artery, and goes to the inferior extremity of the humeral vein. Frequently 

 the ulnar vein is double in the latter portion of its track, and between the 

 two branches lies the artery. It always communicates at this point, by 

 one or more branches, with the deep muscular vein. 



0. Superficial Veins of the Fore-arm. 



Placed outside the fibrous sheath formed by the antibrachial aponeurosis, 

 these veins, which are principally two in number, are maintained against 

 the external face of that membrane by a thin fascia which separates them 

 from the skin. 



A. Median, or Internal Subcutaneous Vein (Fig. 293, 31). This is 



also one of the vessels selected for the operation of phlebotomy. It is the 

 continuation of the internal metacarpal vein, ascends from the inner face 

 of the carpus to the superior extremity of the fore-arm, by crossing the 

 radius in a very oblique manner, and terminates in two very large 

 branches, the posterior of which is the basilic vein, and the anterior the 

 cephalic vein. 



The basilic vein traverses the sterno-aponeurotio (transverse pectoral) 

 muscle, to aid in forming the humeral trunk (Fig. 293, 34). 



The cephalic, or plat vein, crosses the superficial band of the biceps or 

 coraco-radial muscle, is lodged in the space comprised between the levator- 

 humeri and small pectoral muscles, and afterwards opens into the jugular 

 vein (Fig. 293, 35). 



B. Subcutaneous, ok Anteeiok Eadial Vein (Fig. 293, 32). — Less 

 considerable than the preceding, this vein arises at the carpal region, in its 

 course occupies the anterior face of the fore-arm, and terminates in uniting 

 its superior extremity either to the subcutaneous median or the cephalic 

 vein ; the last is most frequently the case. 



6. Metacarpal Veins. 



Three in number, as we know, these veins are distinguished into m- 

 ternal and external collateral of the cannon, and deep or interosseous collateral. 



A. Internal Collateral of the Cannon. — More voluminous than the 

 others, this vein passes from the vicinity of the fetlock along the fiexor 

 tendons, accompanied by the principal artery of the cannon and the 

 external plantar nerve, places itself in the special sheath which envelops 

 the common trunk of the interosseous arteries to the inside of, and behind 

 the carpus, to be continued in the antibrachial region by the median 

 subcutaneous vein, after communicating with the other metarcarpal veins 

 (Fig. 293, 30). 



B. External Collateral of the Cannon.— Situated opposite the 

 preceding— to the external side of the flexor tendons, in company with the 

 corresponding plantar nerve — the external collateral of the cannon follows 

 that nerve to near the trapezium, and then separates into several reticulated 

 branches which anastomose with the internal collateral, from which proceed 

 the ulnar and internal or posterior radial veins. 



