OF THE GREAT ANTERIOR VEINS. 
151 
Hants and Solipeds, as illustrated in the Wild Boar and Guinea Pig-f; in the 
Sheep* * * § '!', Goat*:J:, Ox*'!', Dicotyles;!: and Moschus javensis:|:, and in the Florse'!'. 
It is also present in the common Mole'!'. 
The cross branch in the neck is necessarily present and forms the left innominate 
vein. The left azygos trunk arching over the root of the corresponding lung, de- 
scends in front of it and then turns (like the left vena cava superior in the former 
group) beneath the base of the heart to reach the right auricle, being first joined by 
the great coronary and some other cardiac veins. 
Several gradations in the size of this left azygos trunk are met with in this group, 
which further observation on recent animals would probably render more complete, 
and which conduct by degrees to the third group, where the left venous trunk, re- 
duced to its smallest persistent remnant, receives only veins from the substance of 
the heart. 
Thus in the Hog, the left azygos trunk is very large, and returns the blood not only 
from its own side, but from the lowermost intercostal spaces of the right side also§. 
In the Sheep and Ox it is, comparatively speaking, smaller. Finally, in the Horse, 
it is reduced to a very fine vessel, so that the left venous trunk conveys scarcely more 
than the blood from the cardiac veins ; and in one case I found it quite closed as 
it passed along the left auricle ||. 
This gradual diminution of the left azygos trunk is accompanied by an equivalent 
increase in the size of the right azygos vein. For example : the right azygos is small 
and sometimes even wanting in the Hog ; it is always an insignificant branch in the 
Sheep ; it is very evident in the Ox ; and very large in the Horse. In the last-named 
animal it returns most of the blood from the left intercostal spaces also, and thus 
exhibits the reverse of the condition observed in the Hog ; and approaches, in this 
respect, the characters of the third and last group 
* Eustachius {op. cit. p. 273) describes the left az3'gos in the Ox, Goat, Sheep and Hog, as passing over 
the left bronchus, and states that the coronary vein ends in it. Bartholine, Thom. (Hist. Anat. 84. Cent. ii. 
p. 322) appears to have seen the left azygos in the heart of a lamb. Lancisi (Epist. de vena sine pari, Mor- 
gagni’s Advers. Anat. V. p. 80) mentions the left vena azygos in the same animals as named by Eustachius. 
Ridley (Observat. Medic. Pract. p. 219. In vitulo) says that, in the Sheep and Calf, the azygos is a left 
vein, which he imagined emptied itself into the left auricle or left pulmonary vein. Scarpa (Tabulce Neurolog. 
tab. 7. fig. 4) mentions and also figures the left azygos vein in the Calf “ ending in the trunk of the coronary 
vein.” 
t The Author. J Bardeleben. 
§ Correctly described by Lancisi {op. cit. p. 80). 
11 It is said by Rathke to be absent in the Horse ; and by Bardeleben in the Ass. 
^ The transition from this to the third group is exemplified not only in the Horse and Ass, among Solipeds, 
but also in the Ruminantia; for I find that in the injected heart of the Camel (Museum of the Royal Coll, of 
Surgeons, London, Preparations 111, 112), the only trace of a left azygos visible consists apparently of a rather 
large oblique branch of the coronary vein on the back of the left auricle. The injected heart of the Tapir (Mus. 
Royal Coll. Surgeons, Preparation 105), in which animal Bardeleben says the left azj^gos is wanting, also 
exhibits a similar condition, the oblique vein being so large that it may be a rudimentary left azygos vein. 
