26 ORIGIN OF THE PULMONARY VESSELS IN THE CHICK. 



DESCRIPTION OF PLATES. 



Plate 1. 



Fig. 1. Median-sagittal section (10 m in thickness) through tip of lung-bud of a 20-somite chick, 40 hours' incubation; 

 hematoxylin and eosin stain, series B. Angioblasts, forerunners of pulmonary system, are seen pro- 

 liferating from and near dorsal endothelial wall of sinus venosus. They extend dorsally toward the 

 ventral surface of the gut, which shows a slight ventral swelling the primary lung rudiment. This is 

 about the earliest stage in which there is any evidence of the formation of a pulmonary vascular system. 



Fig. 2. Cross-section (10 m) through tip of primary lung rudiment of a 21-somite chick, 48 hours' incubation; carmine 

 stain, series 0. A slightly later stage in the angioblastic proliferation from the dorsal sinus wall. The 

 right portion of the cell-mass has begun to form a matted group of cells, the tip of the left valve of the 

 sinus venosus. The left portion of the proliferation shows signs of liquefaction by which the common 

 pulmonary vein is formed. 



Fig. 3. Sagittal section (10 m) through left third of proliferation of angioblasts, to show process of liquefaction extend- 

 ing toward sinus venosus. It is about to open into the sinus, thus forming the common pulmonary 

 vein. Hematoxylin and eosin stain; chick of 23 somites, 48 hours' incubation, series D. 



Fig. 4. Median-sagittal section (10 fi) through right two-thirds of mass of angioblasts, to show matting together of cells 

 to form left sinus valve tip. The pulmonary vein is not established. This embryo (22 somites, 44 hours' 

 incubation) is slightly younger than that shown in figure 3. Hematoxylin and eosin stain; series II. 



Fig. 5. Cross-section (10 p) through tip of primary lung rudiment of a chick of 24 somites, 48 hours' incubation; 

 carmine stain, series E. The right two-thirds of the mass of angioblasts has formed the tip of the left 

 valve of the sinus. The common pulmonary vein is now established, opening into the sinus to the left 

 of the valve. Angioblasts can be seen spreading over the ventral surface of the gut. This is the 

 earliest stage in which the common vein is complete. 



Fig. 6. Sagittal section (15 m) through plane of common pulmonary vein, showing it complete, from the sinus venosus 

 to tip of lung rudiment. There is no pulmonary circulation at this stage. Angioblasts can be seen 

 over the surface of the lung-bud. Embryo of 31 somites, 50 hours' incubation; hematoxylin and eosin 

 stain; series X. 



Plate 2. 



Fig. 7. From an injected embryo of 35 somites, 55 hours' incubation, dissected by the paraffin method. The lung 

 consists of a simple ventral diverticulum beginning to show lateral swellings into right and left primary 

 buds. The common pulmonary vein opens into the sinus at the level of the lung rudiment. It drains 

 the capillaries of both cephalic and post-caval portions of the splanchnic plexus. The anastomoses 

 between the plexus and the cardinal veins arc established. The pulmonary arches are not formed, 

 although the dorsal and ventral primordia of the arch are indicated by the blind pouches. The cranial 

 end of the pulmonary artery is now easily recognized in the capillary plexus. 



Fig. 8. A 36-somite chick of 60 hours' incubation, injected with ink and dissected by the paraffin method. Only the 

 right half of the vascular tree is shown. This stage is but slightly older than that in figure 7. The 

 pulmonary arch is now complete but still retains a capillary appearance. The pulmonary artery 

 can be recognized in the cephalic portion of the plexus. The right lobar tributary of the common vein 

 is formed and is connected with its corresponding artery on the dorsal surface of the lung-bud. The 

 cranial tributary of the common vein is plainly seen. The wall of the sinus venosus has been removed 

 to show the opening of the common pulmonary vein into the sinus. 



Figs. 9-10. Dissections of injected chick embryos of 85 hours' incubation. Figure 9 shows the right side of the 

 pulmonary system. In figure 10 the spinal cord, dorsal aorta, and dorsal surface of the gut have been 

 removed, exposing the pulmonary system in a coronal plane from a dorsal view. The lung is in a 

 simple stage of right and left primary buds which do not show further lobulation. The left bud is 

 more ventral than the right and is parallel to the gut. The right bud tends more toward a horizontal 

 position in relation to the plane of the gut. The pulmonary vessels bear a constant relation to the 

 bronchi of the buds, even at this early stage. The artery lies dorsal and lateral to the bronchus; the 

 vein, ventral and medial to the bronchus, the lung capillaries lying between the two on the dorsal 

 surface of the buds. The pulmonary artery comes off from the arch at the junction of its middle and 

 proximal third, and passes directly back to the tip of the lung-bud, where it joins freely, in a capillary 

 net, with the corresponding tributary of the pulmonary vein. Very near the arch a capillary con- 

 nection is given off to the anterior cardinal vein. The two arteries extend parallel to each other and 

 in their proximal third are joined by numerous capillary anastomoses which are drained by the cranial 

 tributary of the common vein. The middle third of the artery has no branches. The entire distal 

 third is connected with the vein by a rich plexus of capillaries over the dorsal surface of the lung-bud. 

 A few twigs are still present, connecting with the post-caval portion of the plexus. The pulmonary 

 vein is made up of several tributaries which unite in a common trunk; this in turn empties into the 

 sinus venosus. Considerable variation is encountered in the pattern of these branches in different 

 specimens. The right and left lobar branches to the lung-buds drain their respective arteries. In 

 figure 9 a vessel connects the right lobar vein to the cranial tributary. This is not constant and is 

 absent in figure 10. A few small branches to the post-caval plexus are seen caudal to the lobar 

 branches. The cranial tributary of the common vein drains the anastomotic vessels between the two 

 pulmonary arteries and arches. It extends directly caudad on the ventral surface of the gut and, 

 with the other tributaries, empties into the common vein. It may have but one opening into the 

 common vein, as in figure 10. This stage is about the oldest in which the cranial tributary is seen 

 complete and represents its highest development. In a later stage, as described by Squier, the cranial 

 tributary loses its arterial connections and disappears. The pulmonary arches (sixth) have undergone 

 rapid growth and have included the arteries within their walls. 



