398 WALTER E. CAMP 



tinuous laterally with the perichondrium of the ceratobranchial 

 cartilage, and medially with the fascia of the coracobranchial 

 muscle. In the cranial part of the gland the sheath thins out 

 and gives way to loose vascular connective tissue. There are 

 no connective tissue septa present, consequently the gland is 

 not divided into lobes or lobules. 



The large vesicles of the adult gland are lined by a layer of 

 tall and narrow columnar cells, many of which are moderately 

 distended with secretion. The nuclei are oval or rod-shaped 

 and stain very intensely. In some parts of the gland the vesi- 

 cles are closely crowded together and their epithelial walls are 

 flattened through pressure. Two small tubules in the dorsal 

 part of the gland, lying on either side of the tubule which con- 

 nects with the true duct described above, are lined throughout a 

 part of their course by a thin layer of stratified squamous epi- 

 thelium. One of the large closed vesicles in the cranial extremity 

 of the gland is also lined by stratified epithelium which has many 

 goblet cells. Another large vesicle has a small rounded ex- 

 tremity which contains so many mucous cells that, when viewed 

 in cross-section, it resembles very closely an ordinary mucous 

 alveolus. The pharyngeal diverticulum mentioned above is com- 

 posed of stratified squamous epithelium directly continuous with 

 that lining the pharynx. The diverticulum, like the epithelium 

 of the pharynx, contains mucous goblet cells in all layers from 

 the membrana propria to the surface (fig. 18). The true duct 

 connecting a part of the gland with the pharynx, is formed by a 

 single layer of columnar cells which become continuous with the 

 basal row of cells of the pharyngeal epithelium. 



ANGIOGENESIS 



The earliest vessels associated with the suprapericardial body 

 are a few small venules which extend into the pharyngo-peri- 

 cardial wall from the inferior jugular vein. In embryos, 33 to 

 36 mm. long, these vessels consist of irregular mesenchymal 

 spaces lined by a layer of developing endothelial cells. At 47.3 

 mm. these irregular spaces or vessels have become more uniform 

 in calibre and are filled with red blood corpuscles. They have 



