406 
DR. M. TONGE ON THE DEVELOPMENT OE THE SEMILUNAR 
Fig. 11. 
Fig. 12. 
Fig. 13. 
Fig. 14. 
Fig. 15. 
Fig. 16. 
forked arterial septum losing itself on wall of artery, e. Aorta, f. Pulmo- 
nary artery. 
From Chick at the 108th hour of incubation, to show the form of the opening 
from the ventricle into the truncus arteriosus. The ventricle has been cut 
across just below the opening and the truncus arteriosus near the centre of 
the vessel. 
a. Slit-shaped opening into truncus arteriosus, b. Thickened lips of slit. 
c. Base of ventricular cavity just below arterial opening, d. Cut edge of ven- 
tricle. 
Portion of truncus arteriosus from Chick at the 115th hour of incubation ; the 
section made through forked margin of septum above and central part of 
vessel below. 
a. Anterior aortic valve-rudiment, b. Anterior pulmonary valve-rudiment. 
c. Commencement of ridge on posterior surface, d. Aortic channel, e. Pul- 
monary channel, f. Line (left edge of anterior aortic valve) followed ante- 
riorly by arterial septum. 
Left side of heart, branchial arches, and part of descending aorta of Chick at 
the 117th hour of incubation. The auricles have been removed. Although 
there is no trace of any division externally, the clots in the vessels show that 
the division between the rudimentary aorta and pulmonary artery has already 
advanced some distance. The absence of the rudiment of the outer semilunar 
valve of the pulmonary artery is shown by the continuity of the clot in that 
vessel with the clot in the undivided portion of the truncus arteriosus. 
a. Ventricle, b. Truncus arteriosus, c. Carotid, d. Aorta, e. Pulmo- 
nary artery, f. Descending aorta. 3, 4, 5. Third, fourth, and fifth branchial 
arteries respectively. 
Heart, branchial arches, and part of descending aorta of Chick at the 117th 
hour of incubation. The auricles removed. The division in the clot marks 
the situation of the upper margins of the semilunar valves at this time. The 
rudimentary trunks are separate up to this point. 
g. Rudimentary semilunar valves. 
Other letters the same as in fig. 13. 
Same preparation turned round so as to show the aorta. The clot in the 
rudimentary aorta is seen, like that in the pulmonary artery, and for the same 
reason, to be cut off from that in the undivided part of the truncus arteriosus. 
Lettering the same as in fig. 14. 
Portion of truncus arteriosus of Chick at the 130th hour of incubation, included 
between sections made just above the valves and a short distance below them, 
showing the interior of the vessel below the valves. 
a. Anterior aortic valve, b. Anterior pulmonary valve, c. Pyramidal 
ridge on posterior aspect of vessel, d. Left edge of anterior aortic valve-rudi- 
