VALVES IN THE HEAKT OE THE CHICK. 
407 
ment, along which the division proceeds anteriorly, e. Pulmonary artery. 
f. Aorta, g. Cut edge of vessel. 
Pig. 17. The same preparation turned, so as to give a better view of the aortic orifice, 
and to show the pyramidal shape of the rudimentary semilunar valves. 
h. Lateral aortic valve, i. Inner aortic valve. 
Other letters the same as in fig. 16. 
Pig. 18. The same preparation turned, so as to give a better view of the outer aortic 
valve. The rounded form of the ridge on the posterior surface and the pyra- 
midal shape of the anterior aortic valve are well seen. 
Letters the same as in fig. 17. 
Pig. 19. Portion of truncus arteriosus of Chick at the 140th hour of incubation, included 
between a section just above the valves and one at the base of the ven- 
tricles. 
a. Aorta, b. Pulmonary artery, c, c. Anterior semilunar valves, d, d. 
Other semilunar valves, e. Septum between aorta and pulmonary artery. 
f. Opening from ventricle into lower part of truncus arteriosus, g. Clot in 
truncus arteriosus below valves. 
Fig. 20. View of upper surfaces of the semilunar valves of the aorta and pulmonary 
artery at the 140th hour of incubation. The inner valve of each artery is 
seen to grow entirely from the side of the thick septum corresponding to the 
rounded pyramidal ridge on the posterior surface ; the outer and anterior 
valves grow from the corresponding parts of the wall of the artery. The 
outer valve in the aorta is seen to be deeply notched. The anterior pulmo- 
nary valve is also slightly notched, and the outer valve very much so, the 
notches in the last fitting corresponding projections of the rudimentary inner 
valve. 
a. Aorta, b. Pulmonary artery, c , c. Inner valves, d, d. Anterior valves. 
e, e. Lateral valves. 
Pig. 21. The same preparation turned over to show the under aspect of the descending 
septum and valves. 
a. Aorta, b. Pulmonary artery, c. Anterior aortic valve, d. Anterior 
pulmonary valve, e. Inner aortic valve, f. Kidge on posterior aspect of 
vessel. 
Fig. 22. Portion of truncus arteriosus remaining between the last section and the ven- 
tricle, showing the arterial aspect of the opening into the ventricle. The 
channel for the pulmonary blood is seen to groove the anterior part of the 
left-hand lip. The slight prominences on the front of the vessel show the 
future position of the bases of the anterior and outer pulmonary valves. 
These are rather exaggerated in the drawing. 
a. Left-hand lip of ventricular opening; its prominent central portion 
becomes continuous with the ridge on the posterior part of the truncus arte- 
