N eee 
F 
5, 
> 
: 
struction of the aortic arches in Lacerta is shown in Fig. 7B and 
that of Perer of the same animal in Fig. 7A. The fifth arch is 
shown in both figures as a division of the sixth. The pulmonary artery 
is shown in VAN BEMMELEN’s reconstruction but not in that of PETER. 
25 
Fig. 7 A. Bio (ab. 
Fig. 7. Reconstructions of the aortic arches of Lacerta. (A after PETER, B after 
-VAN BEMMELEN.) 
The figure of the latter shows a variation in the third arch which has 
lost its connection with the truncus arteriosus. 
In birds, as shown above, the fifth arch is a division of the sixth. 
It bears a close resemblance to the same arch in Lacerta (cf. Figs. 1 
and 7). 
Mammals. The condition of the vascular elements between the 
systemic and pulmonic arches in mammals is of great interest as 
there is apparently conflicting testimony as to their meaning. In the 
human embryo there exists a complete vessel between the systemic 
and pulmonic arches. In the specimen reconstructed and described 
by ZIMMERMANN, it consists of an offshoot from the systemic arch 
— springing from that vessel and uniting again with it. In the two 
cases figured by TANDLER, it arises from the truncus arteriosus and 
empties into the pulmonic 
arch. Fig. 8 is a copy of 
a diagram by TANDLER 
showing the anatomical re- 
Fig. 8. 
Fig. 8. Diagram of the aortic arches in a human embryo about 7 mm long, 
showing the fifth arch extending from the truneus arteriosus to the pulmonic arch 
(after TANDLER). 
Fig. 9. Outline, merely, of a reconstruction by TANDLER of the aortic arches in 
a human embryo just after the division of the conus arteriosus into systemic and pul- 
monic trunks. 
