30 WILLIAM A. LOCY AND OLOF LARSELL 



Cross-sections of these stages were also studied under the mi- 

 croscope and in so far as the territory of distribution is concerned, 

 bear out the observation on the injected specimens studied as 

 transparencies. 



The surface study of a dissected specimen of 6| days incubation 

 (fig. 62) shows very well the connection between the pulmonary 

 artery and the laryngo-tracheal vein. In part I, in a number of 

 instances attention was called to a perpendicular branch (figs. 

 11, 12 and 14) emerging from the pulmonary artery upon its 

 ventral border. Figure 62 shows that this short artery breaks 

 into a network that is recombined into the vein running along 

 the ventral border of the laryngo-tracheal region. This speci- 

 men was imperfectly injected so that the network of blood ves- 

 sels on the anterior dorsal region of the lung did not show as in 

 figure 14, but the connections of the arterial branch and of the 

 laryngo-tracheal vein were well exhibited. The veins from the 

 two sides join into a median vessel which, in turn, unites with 

 the trunk vessel opening into the left atrium of the heart. The 

 branches of the pulmonary vein also unite with this trunk. 



On the eighth day of development, as indicated in part I (figs. 

 14 and 17), surface views of the injected lung show a capillary net- 

 work occupying the antero-dorsal region of the lung, and, by the 

 ten day stage the entire latero-dorsal surface is covered by a net- 

 work of blood vessels. In addition to this there is a well defined 

 denser network of capillaries upon the dorfeal surface. Figure 63 

 from a specimen of the ninth day, shows this denser area of capil- 

 laries from the dorsal aspect. In this figure the central portion 

 of the dorsal region is occupied by a distinctly limited network of 

 capillaries extending in the form of a longitudinal stripe from the 

 cranial to the caudal part of the lung. This vascular develop- 

 ment corresponds in position to the lane-like area (before men- 

 tioned) between the ends of the ento- and ectobronchi as they 

 curve towards each other. It is a characteristic anatomical 

 landmark of all later stages. 



In this sketch an obhque view of the lateral face is exhibited 

 and, on that surface, the capillary network is obviously more 

 scattered than on the dorsal surface. 



