VALVES IN THE HEAKT OE THE CHICK. 
409 
of the pulmonary artery. The anterior and outer pulmonary valves are seen 
extending down the wall of the vessel towards the heart. 
k. Branches from arch of aorta. The other letters the same as in fig. 27. 
Fig. 29. From the heart of the Chick at the 165th hour of incubation. To show the 
mode of union of the lower border of the forked division between the aorta 
and pulmonary artery with the lower portion of the right ventricular border 
of the aperture in the septum of the vehtricles. A horizontal section has been 
made through both ventricles close to the base of the heart, and just below the 
orifice of communication between the ventricles. The truncus arteriosus has 
been cut across just above the rudimentary semilunar valves. The eye looks 
through the base of the right ventricle into the aortic portion of the truncus 
arteriosus and the aperture of the aorta, into which the semilunar valves are 
seen to project. 
a. Orifice of aorta ; the triangular projections are the aortic valves. 
b. Opening of pulmonary artery, c. Rounded ridge with which anterior part 
of lower margin of septal orifice ( d ) becomes continuous, h-e. Muscular sub- 
stance of ventricle, f. Entrance of orifice in septum leading from left to 
right ventricle, g. Base of cavity of left ventricle, i. Cut edge of septum 
ventriculorum. j. Right ventricular orifice of channel in septum ventri- 
culorum, leading into truncus arteriosus. 
Fig. 30. From the heart of the Chick at the 165th hour, much magnified. Its develop- 
ment was further advanced than in the preceding specimen. Preparation and 
position similar to that of fig. 29. 
The growth of the inner valves from the thick rounded ridge is well shown 
in this and the following figure. 
a. Under surface of anterior pulmonary semilunar valve, b. Lower border 
of fork of arterial septum, c. Entrance of pulmonary artery, d. Rounded 
ridge with which anterior part of lower margin of septal opening ( e ) becomes 
continuous, f. Muscular substance of ventricle, g. Cavity of left ventricle. 
h. Entrance of canal in septum leading from left to right ventricle, i. Cut 
edge of septum between ventricles, j. Aperture of canal in septum opening 
into right ventricle, k. Aortic entrance and valves. 1. Base of cavity of right 
ventricle, m. Upper part of margin of septal opening continued into right 
side of forked arterial septum. 
Fig. 31. The same preparation turned over a little so as to show all the pulmonary 
semilunar valves. 
a. Inner pulmonary valve. 1. Inner aortic valve. 
The other letters the same as in fig. 30. 
Fig. 32. From the heart of the Chick at the middle of the 8th day of incubation, show- 
ing the upper surfaces of the semilunar valves, The aorta and pulmonary 
mdccclxix. 3 j 
