OF THE GREAT ANTERIOR VEINS. 
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a coronary sinus receiving veins from the heart alone, as in Man, and in the Monkey, 
Dog and Cat : but amongst those animals which have a left azygos or left superior 
cava, it is certainly absent, as in the Calf, Hog, Sheep, Horse, Ass*, Rabbit and 
Hedgehog. 
III. ANALYSIS OF THE VARIETIES OF THE GREAT ANTERIOR VEINS IN MAN. 
The different conditions of the great anterior veins in the Mammalia having been 
classified according to their progressively increasing deviation from the common ver- 
tebrate type, an attempt may be made, in analysing the varieties of these vessels met 
with in Man, to retrace the series from forms presenting the most complex metamor- 
phosis to such as manifest no fundamental change whatever. In this series the 
ordinary condition of the veins is included as the most frequent actual variety. 
The formation of the cross branch at the root of the neck being regarded as the 
initial step in the metamorphosis of this portion of the human as of the mammalian 
venous system, the varieties of these veins in Man may be divided into two classes, 
according to the presence or absence of this transverse branch. 
The occurrence, in one or another degree, or the entire failure of the subsequent 
stage of the metamorphosis, viz. the occlusion of one of the lateral primitive veins, 
suffices to distinguish the first class of varieties into three groups, corresponding with 
those already indicated as the regular conditions in different Mammalia. A. In the 
first group, comprehending the normal condition, in which the occlusion is of the 
greatest known extentT, the persistent portion of the vein, after metamorphosis, con- 
veys only the blood from the substance of the heart, and forms a cardiac venous 
trunk. B. In the second, it would also return the blood from its own side of the 
thorax, and thus constitute an azygos venous trunk. C. In the third, where no occlu- 
sion occurs, it transmits the blood from the whole of its own side of the upper part 
of the body, and is then a second vena cava superior. 
In all of these cases, one of the lateral primitive veins is developed into the ordi- 
nary vena cava superior, and in most instances this is the vein of the right side, whilst 
that of the left undergoes metamorphosis ; but the reverse of this may happen, as 
* Reid (Art. Heart, Cycl. Anat. and Phys. p. 597). 
t It has already been shown that complete occlusion of this primitive vein (i. e. from the neck down to its 
entrance in the right auricle) does not (as Rathke supposed) occur, in the ordinary condition, even of the 
highest Mammalia or of Man, nor has it yet been seen as an occasional variety. That it ever does happen is 
scarcely probable ; for just as in the utmost known amount of abnormal obliteration of the inferior cava, the 
hepatic veins always concur to form a short inferior trunk, which opens into the right auricle, so the confluence 
of the coronary and other cardiac veins may set a like limit to the occlusion of the left anterior primitive venous 
trunk. Nevertheless, it is possible that the process might extend to the closure of its lower end or coronary 
sinus also, the blood from the substance of the heart then returning to the right auricle directly through en- 
larged anterior or posterior cardiac veins, or taking some altogether different course. In a curious case re- 
corded by Le Cat, and hereafter to be particularly mentioned, the auricular end of the left primitive vein 
seems really to have been closed, though its channel continued pervious up to the neck. 
MDCCCL. X 
