VEINS OF MAMMALIA. 55 



these reservoirs of blood at the depths to which they retreat when 

 harpooned^ explain the profuse and lethal haemorrhage which 

 follows a wound that, in other Mammalia, would not be fatal. 



In the Ungulates a left azygos co-exists with a single (right) 

 precaval. In the Hog the azygos trunk passes forward^ left of the 

 aorta, crossing that vessel below the arch and curving over the 

 left auricle, and enters the right. Hunter notices its attachment 

 to the left auricle and its analogy, in both the Hog and Fallow- 

 deer, to the left precaval in Birds. 1 In the Corinne Antelope (A. 

 Dorcas) Hunter observed 6 two azygos veins, the left being the 

 larger' ; 2 a right azygos exists in the Ox, and is larger in the Horse, 

 receiving blood from several of the left intercostal spaces. The 

 oblique vein at the back of the left auricle is large in the Drome- 

 dary and Tapir, and represents the remnant of a left azygos. The 

 portal vein shows valves in some Ruminants. In the Rhinoceros 

 the right precaval receives the right or common azygos close to 

 its termination at the upper part of the right auricle : two inches 

 above this it receives the risjht vertebral vein which is about half 



o 



an inch in diameter ; two inches above this it is formed by the 

 junction of the left brachiocephalic. At the concavity of the great 

 vein formed by this junction, the bronchial veins and some small 

 pericardia! veins enter. The upper part of the precaval receives 

 the two large jugular veins close together, so that a proper ( vena 

 innominata ' can scarcely be said to be formed. The left vena 

 azygos, which is formed by the union of a few intercostal veins 

 of the same side, terminates in the left subclavian vein, which re- 

 ceives separately the left vertebral vein from the neck. The 

 right or principal azygos receives the intercostal veins of both 

 sides as far forwards as its entry into the precaval vein : the 

 Rhinoceros in this structure agrees with the Horse. The coro- 

 nary vein receives a small pericardial vein, which descends along 

 the back of the left auricle, before it terminates with the inferior 

 cava, at the base of the right auricle. 



With the relatively long and narrow thorax of the hoofed and 

 most other Mammals the pre- and post-caval trunks are correspond- 

 ingly longer than in Man ; the length of the thoracic part of the 

 post-caval being as is the distance of the right auricle from the dia- 

 phragm, and also from the dorsal region : the base of the heart 

 being further from the back as well as from the midriff than in 

 Man. 



In Carnivora, Quadrumana, and Bimana the blood from the 



1 ccxxxvi. vol. ii. pp. 124, 140. 2 Ib. p. 147. 



