166 
MR. MARSHALL ON THE DEVELOPMENT 
to show the large valve x, at the mouth of the great coronary vein (g), and smaller 
valves at the mouths of the posterior {p, p) and middle {m) cardiac veins, t. Orifice 
of the coronary sinus into the right auricle, with the Thebesian valve, o, /, v. Re- 
mains of the left primitive venous trunk above the coronary sinus, consisting of o, a 
small oblique auricular vein ; I, lines or streaks on the wall of the left auricle; and v, a 
small duplicature of the serous layer of the pericardium, passing between the left pul- 
monary artery and the subjacent pulmonary vein, which is referred to in subsequent 
plates as the vestigial fold of the pericardium. 
Fig. 2. Sketch of the back of the Sheep’s heart ; the great vessels being cut off 
short. 1, 2 , 3, 8, 10, 10, c and e refer to the same parts as in fig. 1. s,d. The trunk 
of the left azygos vein laid open, showing the large valve (j:) at the entrance of the 
great coronary vein (g), and the smaller valves at the mouths of the veins marked 
p, m,p. The portion of the left azygos vein marked s\ is analogous to the coronary 
sinus in Man, s, fig. 1. t. Orifice of the left vena azygos, destitute of a Thebesian 
valve. 
PLATE II. 
Development of the great anterior veins in the embryo of the Sheep. Each figure 
is magnified two diameters. Corresponding letters of reference are used in common ; 
viz. a. The right, and a', the left primitive jugular vein ; o, the occluded portion of 
the left primitive jugular vein. h. The right, and b', the left cardinal vein. c. The 
right, and c', the left canal of Cuvier, d. The transverse branch across the root of 
the neck, afterwards the left innominate vein. e. The trunk of the future vena cava 
inferior. 1. The right auricle. 2. The left auricle. 3. The ventricles. 4, 4'. The lungs, 
right or left. 5, 5'. The Wolffian bodies, right or left. 7- The stomach. 
Figs. 1, 2, 3. Lateral and front views of an embryo, -l^ths of an inch long. The 
great anterior veins are symmetrical, and consist of four lateral trunks, viz. two jugu- 
lar and two cardinal veins, ending in the two Cuvierian canals. The jugular veins are 
short and vertical; the cross branch is wanting, but two little points are seen pro- 
jecting from the inner side of the jugular veins where this transverse vessel is to 
appear. The dotted lines in figs. I and 3 indicate the outline of the liver, which has 
been removed. 
Fig. 4. Embryo, ^^ths of an inch long. The jugular veins elongated, and begin- 
ning to approach each other opposite the place of the future transverse branch, which 
could not be traced quite across the neck. The cardinal veins are smaller, owing 
to the wasting of the Wolffian bodies. 
Fig. 5. Fleart of an embryo, 1 inch long. The cross branch distinct, consisting 
of a fine vessel, which is wider at each end than in the middle. 
Fig. 6. Embryo, -|^ths of an inch, and fig. 7, embryo, 1-^ths of an inch long. The 
jugular veins have become more closely approximated at the root of the neck. The 
