SANGUIFEROUS SYSTEM. 515 



jugulars formed chiefly by the temporal and internal maxil- 

 lary veins, and receiving the blood from the external and 

 lower parts of the neck, enter likewise the subclavian veins, 

 exterior to the former. In many of the inferior quadrupeds, 

 especially in all the hybernating tribes, the venous blood is 

 returned from the brain, not by the internal jugulars, but 

 from the anterior ramus of the lateral sinuses, through the 

 temporal canal on each side, into the external jugular veins, 

 and also by the vertebral veins which here unite with the 

 external jugulars. 



From the anterior extremities, the blood is returned by 

 the cutaneous radial and ulnar, or the cephalic and basilic 

 veins, and by the deeper-seated anastomosing brachial veins 

 which accompany the corresponding arteries throughout 

 their ramifications, each artery being accompanied by two 

 veins which freely anastomose with each other around that 

 vessel. The union of these veins from the arm, forms the 

 axillary, on each side, which, after becoming enlarged by the 

 addition of numerous scapular and thoracic branches, is con- 

 tinued into the subclavian. The two subclavian veins, after 

 receiving the internal and external jugulars and the two 

 vertebral veins which follow the course of the vertebral arte- 

 ries, become the brachio-cephalic trunks (142. A. B. a. b.), 

 which form, by their union, in most mammalia, the superior 

 vena cava (142. A. c.) In many of the inferior species of 

 mammalia, however, as among the rodentia, monotrema, 

 marsupialia, and in the elephant, the hedgehog, and some of 

 the chiroptera, the brachio-cephalic veins continue separate 

 to the right auricle, thus constituting two distinct superior 

 cav(B, as found in birds and reptiles, and occasionally as an 

 abnormal character in man. The brachio-cephalics receive 

 also the inferior thyroid, and the internal mammary veins ; 

 and the superior vena cava, formed by their union, receives, 

 in its course to the heart, some small pericardial and medias- 

 tinal branches, and the great vena azygos, which establishes 

 important communications with several branches of the 

 inferior cava. The vena azygos, in the ornithorhynchus, 

 where the superior cava is double, opens into that of the left 

 side. The blood conveyed by the coronary arteries to 

 nourish the heart, is returned to the right auricle (142. A. d.), 

 chiefly by one great coronary vein, which enters the back part 

 of that cavity near the septum auricularum ; where the 



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