302 ALBERT KUNTZ 



The exact course of the development of the myenteric and the 

 submucous plexuses in the walls of the intestine is not easily deter- 

 mined. Cells apparently migrate posteriorly in the walls of the 

 intestine from the anlagen of the myenteric and the submucous 

 plexuses in the anterior region of the digestive tube. On the other 

 hand, as already indicated, cells migrate ventrally from the an- 

 lagen of the prevertebral plexuses in the posterior region of the 

 body and become aggregated along the walls of the rectum. There 

 is no evidence of the migration of cells from the anlagen of the 

 prevertebral plexuses into the walls of the digestive tube farther 

 anteriorly until the anlagen of the myenteric and the submucous 

 plexuses have become well established. The evidence at hand 

 seems to indicate that in the anterior region of the intestine the 

 myenteric and the submucous plexuses arise from cells which 

 migrate peripherally along the paths of the vagi, while in the pos- 

 terior region at least some of the cells taking part in the develop- 

 ment of the sympathetic plexuses in the walls of the intestine 

 wander down from anlagen of the prevertebral plexuses. 



c. Pulmonary plexuses. In transverse sections through the 

 region of the lungs of embryos of Thalassochelys caretta at about 

 the fifteenth day of incubation branches of the vagi appear to 

 be closely associated with the bronchi as the latter enter the tissues 

 of the lungs. Cells wander in along these branches and give rise 

 to the anlagen of the pulmonary plexuses. 



d. Cardiac plexus. In transverse sections through the anterior 

 region of the heart of embryos at about the seventeenth day of 

 incubation the mesocardium lies far to the left. In this region a 

 fibrous branch accompanied by numerous cells may be traced 

 ventrally from the left vagus trunk into the dorsal wall of the left 

 atrium where many of the accompanying cells become aggregated 

 to form the anlagen of the cardiac plexus in this region (fig. 12, 

 C.P.). In transverse sections a little farther posteriorly in embryos 

 of the same stage the mesocardium lies ventral to the oesophagus. 

 In this region fibrous branches accompanied by numerous cells 

 may be traced from both the right and the left vagus trunks into the 

 dorsal wall of the heart where cells become aggregated to give rise 

 to the anlagen of the cardiac plexus in this region (fig. 11, C.P.). 



