OF THE GREAT ANTERIOR VEINS. 
145 
the yet undivided auricle, and is drawn with it, in the general movement of the heart, 
over to the right side. This being premised, it is easy to follow the changes which the 
lower pervious portion of the left canal of Cuvier undergoes, after the complete occlu- 
sion of its upper part, represented now by the opake streak (fig. 9, 1) on the wall of 
the left auricle, and by the minute fold of the pericardium {v) already described. For 
a time, the lower part of this canal persists as a conical pouch (Plate III. figs. 5, 6 , c ') ; 
but subsequently (Plate IV. figs. 7, 8, from an embryo, 2^ inches long) this conical 
venous channel becomes elongated ; its upper part forms the oblique vein already 
mentioned, whilst its lower part {s) pursues its course to the right along the auriculo- 
ventricular furrow. The coronary vein (g), properly so called, is now seen to end, 
not in the right auricle itself, but in this venous channel^ falling into its under side at 
an acute angle, at a short distance from its termination in the auricle. Still later, in 
a foetus 5 inches long, from vertex to coccyx, the same facts are as plainly observed 
(figs. 9, 10) ; and on cutting open the veins at this period, a narrow oblique venous 
channel (o), tapering to a point as it ascends to the left along the back of the auricle, 
may be traced from the point of entrance of the true coronary vein (g) upwards to 
the opake streak (/), seen on the wall of the auricle; whilst below the entrance of the 
coronary vein, the venous channel becomes dilated {s) as it passes to the right, re- 
ceives several cardiac veins, including generally the middle cardiac, and ends in the 
lower part of the right auricle, close to the interauricular septum, by a somewhat 
contracted orifice, which is guarded by a rudimentary valve. This wider lower por- 
tion of the persistent venous channel can even now be recognized, in all respects, as 
the coronary sinus, and the valve beginning to form at its auricular orifice is the 
Thebesian valve. The opening of the true coronary vein into it is marked by a 
sharply-ridged margin, but as yet there is no valve there. 
As development advances to the full period of foetal life (fig. 11), the proper 
coronary vein (g), and the coronary sinus {s), become gradually more continuous in 
direction than heretofore, but the difference between them can be easily discerned, 
even externally. The muscularity of the sinus, as distinguished from the vein, be- 
comes evident, and the opening of the latter into the former is protected by a valve, 
the two segments of which are for a time narrower in proportion than in the adult. 
Above the entrance of this vein into the sinus, a rounded recess leads upwards and 
to the left into the small oblique vein (o), which, taking the course of the primitive 
vessel, of which it is evidently the remnant, runs along the back of the left auricle, 
about half-way to the root of the pulmonary veins, and there ends in the opake 
streak (/) previously mentioned. This small oblique vein is crossed superficially by 
the muscular fibres of the left auricle; it is peculiarly straight in its course, and 
receives tortuous branches from the walls of the auricle. 
MDCCCL. 
u 
