464 



WILLIAM A. LOCY AND OLOF LARSELL 



dimensions dorso-ventrally and when viewed from the side is 

 rectangular in outline. It also occupies a more lateral position 

 in the thoracic cavity. The lung has begun to press against the 

 ribs and exhibits shallow furrows where the lung substance has 

 grown around the bodies of the ribs. The five air-sacs, two on 

 the anterior and three on the ventral margin, are formed and 

 project beyond the surface of the lung. As indicated above, the 



-;- Pul.At. 



B 



Fig. 15 (A) Dissection of the left side oi an cnilnyo during tlic last half of 

 the seventh day of incubation, the fourth aortic is much atrophied on this side. 

 (B) Heart and right lung of the same specimen. The fourth aortic arch is larger 

 on this side and separated from the third. Projections of the cervical and ab- 

 dominal air-sacs are exhibited. Drawn by G. H. A. Rech. 



posterior intermediate is the last of the air-sacs to expand and 

 project beyong the lung wall. The cervical, and interclavicular 

 sacs are smaller, but both project from the lung wall earlier than 

 the posterior intermediate. The part of the interclavicular sac 

 showing in figure 16 is only the lateral moiety of the sac, the 

 mesial moiety, which at this stage is separate and independent, 

 can not be seen from this aspect. 



