134 
MR. MARSHALL ON THE DEVELOPMENT 
that vessel (see Plate I.). Into the extremity of the coronary sinus, as thus defined, 
the great coronary vein (g-) may be said to open, its entrance being guarded by the 
valve alluded to; and along the lower border of the sinus there enter three or four 
venous branches {p, p, p), which ascend from the back of the ventricles, one of 
them generally forming the middle cardiac vein (m) ; the mouths of these branches 
are also almost invariably provided with fine valves consisting of one or two segments, 
but beyond the coronary sinus and the larger valve first noticed, no more valves are 
met with either in the trunk of the principal cardiac or coronary vein, or in any of 
its tributary branches. 
In the hearts of the Monkey, Cat and Dog, a precisely similar arrangement is ob- 
served. 
In those animals which possess a left vena cava superior, the great cardiac or 
coronary vein ends in that additional venous trunk, as seen, for example, in the Mar- 
supialia, many of the Rodentia, and in the Elephant. Moreover in cei’tain Ruminant 
and other animals, as for example the Sheep (Plate I. fig. 2), in which a large left azygos 
vein exists, arching over the root of the left lung and thence pursuing the same 
course to the right auricle as the left vena cava superior in the cases already alluded 
to, the coronary vein (g) opens into this azygos venous trunk {ss'). In both these two 
conditions, as I have observed in the Rabbit, Hedgehog, Ox, Sheep and Pig, the lower 
part of the large left venous trunk is always dilated and muscular, and at the opening 
of the coronary vein into it, there is found a large valve composed in some cases of 
one segment {x), and in others of two. A series of small veins {pmp), ascending 
from the back of the heart, join it at intervals between the valved entrance of the 
coronary vein and the opening' of the venous trunk itself into the right auricle ; and, 
lastly, the mouths of these ascending cardiac veins are for the most part regularly 
provided with valves, whilst, on the contrary, no valves exist along the continuation 
upwards of the large venous trunk, at least in the neighbourhood of the heart ; nor 
are valves met with, as a constant condition, in any other part of the cardiac veins 
themselves. 
On comparing, in Man and Animals, the arrangement of these vessels and the dis- 
position of their valves, I was led to conjecture that the dilated and somewhat muscular 
portion of the coronary vein, usually named the coronary sinus (Plate I. fig. 1, a-), together 
with its large and important opening {t) into the right auricle, as seen in Man and 
such of the higher Mammalia as have no left vena cava superior or left azygos vein, 
was strictly analogous to the expanded lower portion (fig. 2, s') and auricular orifice 
(0 of those additional left venous trunks, as found in other quadrupeds; and, in fact, 
that it ivas the persistent lower part of the left anterior primitive venous trunk. 
On this supposition, the coronary vein proper, in Man and the higher Mammalia, 
might be said to end in the so-called coronary sinus, at the valved orifice above de- 
scribed ; and thus its mode of termination, instead of varying in different cases, would 
be similar throughout the entire mammalian series, — the vessel in no case reaching 
