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nections between them and the anlagen of the plexuses in the walls 

 of the digestive tube. 



In embryos 16 mm in length the vagus trunks as well as their 

 branches, many of which have established connections with the plexuses 

 in the walls of the digestive tube, are apparently free from wandering 

 cells. In the walls of the oesophagus the cells which have wandered 

 in are aggregated into more or less distinct groups arranged in two 

 broken rings. The myenteric and submucous plexuses are thus becom- 

 ing distinct. A similar arrangement, though less definite, is apparent 

 also in the walls of the intestine. Fibrous connections have become 

 established with the ganglia of the sympathetic trunks as well as with 

 the coeliac and hypogastric plexuses. It is interesting to note that 

 all these sympathetic nerves still contain numerous cells which are 

 apparently migrating peripherally along their courses. It is probable, 

 therefore, that cells wander down from the ganglia of the sympathetic 

 trunks into the myenteric and submucous plexuses after these fibrous 

 connections are established. 



2. Pulmonary plexuses. 

 In transverse sections of »embryos 6 and 7 mm in length in the 

 region of the bifurcation of the trachea, some of the cells which wander 

 from the vagus trunks toward the oesophagus are observed to be 

 carried out along the anterior and dorsal surfaces of the bronchi. 

 These cells obviously constitute the anlagen of the pulmonary plexuses. 



3. Cardiac plexus. 

 The first unmistakable evidence of ganglia pertaining to the cardiac 

 plexus is found in embryos about 12 mm in length. In transverse 

 sections through the anterior region of the heart small groups of 

 nervous elements are observed ventral to the trachea (Fig. 2 eg.), a 

 few of which have penetrated deep into the angle between the aorta 

 and the pulmonary artery. This condition may be traced through a 

 short series of successive sections in this region. These cell-aggregates 

 constitute the anlagen of the earliest ganglia of the cardiac plexus. 

 They are still without fibrous connections, but a few short fibrous 

 branches are seen to arise from the vagus trunks and the left recur- 

 rent branch and extend toward the heart (Fig. 2 cb.). These are 

 obviously the earliest cardiac nerves. Their fibers are still loosely 

 aggregated and are accompanied by numerous cells, some of which 

 appear to escape from the tip of the nerve and migrate toward the 

 anlagen of the cardiac ganglia in advance of the growing fibers. 



